So I recently began a D&D campaign that, so far, has been a fairly hack n slashy romp with a bit of roleplay.  Im newish to 5e and decided to play an Arcane Trickster with ritual caster.  The party consists of a barbarian, myself and a ... Bard.  I apologize in advance for the rant I am about to embark on but I'm finding myself so frustrated that I actively dont want to level up because every time I do my character feels weaker.

#begin Rant#

I loathe the 5e bard class.  It makes my brain bleed that a bard is as good of a caster as a wizard.  They are also a skill monkey.  They literally can do everything in the game except slaughter things with a sword ( assuming they dont build for it in which case they can : | ). The bard is the kid on the playground who "has all the powers".  As an arcane trickster I kept finding that any situation in which my utility came into play - the bard has the same utility or better.  

I thought I could differentiate from the bard enough mechanically by sticking to one side of the spell list.  Unfortunately, the list of spells is not nearly big enough to avoid constant bard overlap. The campaign is not giving me any opportunities to be the sneaky investigating problem solver skill monkey I wanted him to be - And when it does I have to compete with the Bard.  Instead, it is a relatively basic questing and lots of combat. I decided to take 2 levels of wizard so that I could bring more of the arcane flavor to my character, however, ive realized that I keep misunderstanding the multiclass rules and my character gets weaker the more I know.  For instance, even though my entire backstory is that I'm a high intelligence rogue who studies arcane magic for the purpose of achieving my goal, who is part of an arcane espionage org, and who has ritual caster and even though I have level two spell slots, I cannot cast a level 2 wizard spell that is in my spellbook.  This makes so little narrative sense to me that I want to claw out my eyes.  Additionally, there is almost no magic that actually increases my potency in melee so I cant play what I had hoped would feel more like a roguely eldritch knight.  I can get spells that help me stealth but Im already so good at stealth its too easy to have advantage every turn and im just losing sneak attack die by taking wizard levels. ( really,  attacking someone who is next to my ally is the exact same as attacking someone who I have blinded and rendered helpless? REALLY!? smh ) Meanwhile the barbarian has two attacks.  I could use higher spell slots to boost spell damage... or I could deal *more* damage with sneak attacks that dont require limited spell slots... I am feeling really hampered by the D&D rules here.  

I wanted to play a tactician who uses magic and guile to control the situation and deal high burst damage but be a severe glass cannon.  I dont see a way to build this character and I dont know which direction to go.  I need to find my character's niche but I think the versatility implied by my backstory of "arcane espionage" runs against having a niche at all.  I dont want to be better in combat than the barbarian who now gets two attacks and I dont need to be a more powerful spellcaster than the bard - but i want there to be *something* that my character is best at.  Right now all I have there is sneaking which feels pointless in 95% of our encounters and becomes much less important once the bard gets invisibility *sigh*

Sorry for the rant / Not about calling Bards dumb

So in conclusion

1 ) Why have we not all agreed to murder bards on sight?

2 ) How should I build this character to maximally avoid overlap? Wiz 2 / AT forever? Ask my DM to retcon into straight AT and just be a darn rogue with a light splash of flavor? Or would a Wizard with 3 levels of AT eventually be something other than a wizard who lost 3 levels to a sneak attack he will never use? Or should I just stop thinking about how much the D&D rules get in my way, be less powerful, and push my group to roleplay? Yeah probably that last one but advice would be welcome.  

Quote from Noxid86>>

I loathe the 5e bard class.  It makes my brain bleed that a bard is as good of a caster as a wizard.  They are also a skill monkey.  They literally can do everything in the game except slaughter things with a sword ( assuming they dont build for it in which case they can : | ).

No Bard subclass is on par with real martial classes when it comes to killing things with a sword, nor are they particularly good at killing things with magic either. And while their spell selection is fantastic, as an Arcane Trickster you should be well acquainted with how limiting having a fixed number of Spells Known can be. While they really can do almost everything, every bard has to pick a very narrow slice of "everything" to focus on.

I thought I could differentiate from the bard enough mechanically by sticking to one side of the spell list.  Unfortunately, the list of spells is not nearly big enough to avoid constant bard overlap.

A 1/3rd caster (or heck, even a 1/2 caster) doesn't have the spell slots to spare to solve the party's problems with magic. You really shouldn't be trying to compete on those terms. Instead, use magic to be a more effective Rogue, which is something the Bard can't do. Also, ask the bard if they can help you! Haste or Faerie Fire would do wonders for you in combat.

The campaign is not giving me any opportunities to be the sneaky investigating problem solver skill monkey I wanted him to be - And when it does I have to compete with the Bard.  Instead, it is a relatively basic questing and lots of combat.

This is partially the DM's fault. Everyone should've come to a mutual understanding about what kind of game they wanted to be playing before starting a campaign. It sounds like you and the DM had different expectations.

I decided to take 2 levels of wizard so that I could bring more of the arcane flavor to my character, however, ive realized that I keep misunderstanding the multiclass rules and my character gets weaker the more I know.

Yes, the multiclassing rules are particularly cruel to partial casters. I'd ask your DM nicely if they could let you go back to being a full Rogue. The multiclassing rules can create very powerful combinations but it's also really easy to shoot yourself in the foot if you don't fully understand the implications.

Additionally, there is almost no magic that actually increases my potency in melee so I cant play what I had hoped would feel more like a roguely eldritch knight.

Have you considered Shield, Absorb Elements, Mirror Image, Shadow Blade, Booming Blade or Misty Step? There's plenty of melee combat utility spells. Shadow Blade in particular is extremely strong for a Rogue.

I can get spells that help me stealth but Im already so good at stealth its too easy to have advantage every turn and im just losing sneak attack die by taking wizard levels. ( really,  attacking someone who is next to my ally is the exact same as attacking someone who I have blinded and rendered helpless? REALLY!? smh )

How does high Stealth give you advantage every turn while you're in melee range? Is the DM letting you hide in plain sight? If you have some external source of advantage, have you considered using two-weapon fighting?

I wanted to play a tactician who uses magic and guile to control the situation and deal high burst damage but be a severe glass cannon.  I dont see a way to build this character and I dont know which direction to go.  I need to find my character's niche but I think the versatility implied by my backstory of "arcane espionage" runs against having a niche at all.  I dont want to be better in combat than the barbarian who now gets two attacks and I dont need to be a more powerful spellcaster than the bard - but i want there to be *something* that my character is best at.  Right now all I have there is sneaking which feels pointless in 95% of our encounters and becomes much less important once the bard gets invisibility *sigh*

Invisibility isn't going to remove the need to be good at Stealth. It lets you attempt to be sneaky any time, anywhere, but you still have to be sneaky. And if the rest of the party hasn't invested significantly into Stealth, that means you're the only one that's likely to get away with sneaking around. The thing about sneaking around is that the group is only as good at it as its weakest link.

2 ) How should I build this character to maximally avoid overlap? Wiz 2 / AT forever? Ask my DM to retcon into straight AT and just be a darn rogue with a light splash of flavor? Or would a Wizard with 3 levels of AT eventually be something other than a wizard who lost 3 levels to a sneak attack he will never use?

I'd go full Arcane Trickster, or if being a Rogue isn't working for you, I'd consider changing to a Bladesinger Wizard, Hexblade Warlock or College of Whispers Bard.

Well, unfortunately I am comparatively new to 5e also, and I'm playing a Bard while occasionally giving my son advice on writing content for his games.  I'm pretty old school and back in AD&D days you had to play for about ten levels before you could become a bard, who was a bit of a fighter, thief and druid, all rolled into one.

As a Rogue you are the stealth guy.  You are the pick the locks guy.  You are the "I get crazy damage when I stab you from the shadows" guy.  Is that what you wanted to be when selected Arcane Trickster?  If you have a Bard in your party, you should stop trying to be the Bard guy.  He's likely to be a better Bard than you, which is OK.

As it happens, the Rogue in my party chose Performer background and he tries to be a better Performer than me.  The problem is he needs to pour skill and focus into Dexterity and stealth and I'm good with pouring effort into Charisma and performance.  Every encounter, and I mean every combat encounter, he runs off and tries to stealth so he can get sneak attack damage with advantage.  The guy could be fighting on an acre sized basketball court wearing Mickey Mouse Ears and he would still announce, "I run off and hide."  Well, I'd hide too, but for a different reason.

We hit fourth level and I decided he was going to do this no matter what, so I decided, I better help him.  So I picked up invisibility and silence spells so I could give the guy even more of what he needs.  One of the other party members picked up Enhance Ability, which has uses in and out of combat.  The only problem with using E-A in combat is deciding whether you have a better spell, which you probably do.  We picked up these spells to help others in the party be better at what they do.

The moral of my story is stop trying to be a better bard than the bard and discuss with him how he might help you out, and you help him out.  As a bard it sucks to be stuck with an AC of 14 and a pointy stick (rapier).  So you definitely got something better than the bard, stealth and sneak attack.  Make that the thing you bring to the party.  And next time, play a Bard.  You might enjoy being a bard, but I bet instead you will find out it isn't better FOR YOU than the character you wanted to play.  I haven't played a Rogue, so I can't tell you why you feel you're getting weaker.   Good luck - Have Fun - Stay Healthy

I'd recommend going straight rogue. You can't really go wrong there, and you with your sneak attack dice will out-damage a bard anytime. If you multiclass, you CAN go wrong, and it sounds like you did - you can end up picking options that don't help, and then you've basically just skipped levels, with the option of pretending to play as a level 2 wizard, whoo so much power. (If you go straight one class, then the natural improvement of the class just makes it so you can't really go TOO far wrong with choices. Your sneak attack dice will keep going up.)

Rogues in 5e are excellent glass cannons. Hide, get advantage for your sneak attack, roll all the D6s at the table. The bard cannot do this.

You can use your AT to support what rogues are good at - stealth, stabbing. For example, you can take mage hand for poking traps, then take either Find Familiar (for a permanent ally around, to give you advantage and sneak attack all the time!) or Shield (so that even if you do get attacked, you can hold out for a hit or two, make yourself less glass of a cannon). Or Silent Image because everyone gets more sneaky when they can make enemies see things that aren't there.

Definitely go straight arcane trickster if you can, MC wizard makes you a bad rogue and a bad wizard.  if you can't just keep your two levels of wizard and push rogue.  Switch up your tactics, booming blade for example could be a great asset for you, depending on how your team fights.  If it were me, I'd probably use a bow, and use my spells to help me hide so I can sneak attack.

What it really sounds like you're looking for though is to be a sneaky wizard.  See if your DM will let you retcon to a full wizard.  Take the criminal/spy background and boom, now you're a sneaky wizard, and you have the magical arsenal to BE that character who's in control of the situation. What's the situation?  Does.  Not.  Matter.  You have a spell for that.

That's as arcane espionage as you can get.  Get find familiar, and send it to spy for you.  You'll have thieves tool proficiency and stealth when you need to sneak.  If something is dumb enough to roll up on you in melee range, you can shadowblade/booming blade them straight in the face if you so desire.  The bard can steal /some/ of your spells with magical secrets, but certainly not /all/ of them.  You /will/ find plenty of things that he simply cannot do.

I'm really curious what bardic college the other player chose, if his spells and skills overlap with yours so often. 

To be honest, I think step one for you is to have an honest conversation with the DM about your frustrations. If a player is feeling stifled and isn't having fun, it's a problem - especially if he's one of three people in a party. The entire point of D&D is collaborative storytelling, so if you aren't getting an opportunity to participate in that story, it ultimately falls to the DM to rectify the situation. In order to do that, though, he needs feedback from you. 

As for your multiclass woes, I can sympathize. I'm a glass cannon Ranger/Cleric, so I know all too well what you sacrifice when you halt progression in partial-caster class to take a few levels in full caster. Multiclassing is great for 1) adding versatility you wouldn't otherwise get in your base class, 2) complementing skills at the core of your base class (not your subclass),  and 3) taking RP/character development in a new direction. It is not great for making yourself good at something your base class was never designed to excel in. And the tradeoff of versatility is that, ultimately, you make your build weaker. If you're looking to find your niche, adding more magic to your character isn't gonna do it, especially not when your party includes a mage who literally has a class feature called Jack of All Trades.

From the description of your campaign, it doesn't sound like sticking with a multiclass will do anything but frustrate you more. I agree with the others that you'll be happier focusing on being a better rogue. Or, if it's a lost cause and the DM won't make adjustments to your liking, maybe your Arcane Trickster leaves on his own adventure and you roll up a new character?

For what it's worth, I love your character concept. I hope you can make it work without ditching him entirely! If you can't, I echo the suggestions above for gishier builds (Bladesinger, Hexblade, College of Whispers) and also recommend for your consideration a Gloomstalker Ranger with either a Criminal or Spy background. Best of luck!

Lore likely.  They are massive skill monkeys, and quite powerful.

There's a bit to unpack here. I do feel you, though. Bards being full casters also kind of tripped me up with my first serious 5E character. I wanted to make a charming duelist who used magic to enhance his swordplay so I went Swords Bard. After about 4 levels I realized that most of a Bard's power comes from their spellcasting and that even a Sword's Bard was lacking in the swordplay area, so I ended up dipping one level in Hexblade and then going full Swashbuckler Rogue. Now I have the character I want. That was a little tricky, though, and it's much easier to multiclass yourself badly than it is to do it well.

So here are my suggestions for you:

1. I will concur with everyone who said you should ask to retcon your levels in Wizard and go fully Arcane Trickster. Taking levels of Wizard is an example of an awkward multiclass, mechanically.

2. Maybe remind the Bard player that they are the only ones with any capacity for healing and cleansing magic in your party. Don't pressure them to do it, but just put it out there that it's definitely a niche they could fill.

3. Take a bit to think about your character abilities and the play style they suggest. If you get your narrative and your mechanical aspects to sync up with each other and jive, it'll do wonders for making you really inhabit a character. Sometimes a really strong style and flavor of a character make them stand out even if mechanically they might look similar to something else. I took your concepts of Arcane Trickster, Ritual Caster, and "Arcane Espionage Organization" and rolled them around in my head and a pretty distinct character came out of it. What I see is a character that is subtle, patient, and methodical. They took the time to become a ritual caster by the gods, which is the slowest and most painstaking form of magic there is. This character is not afraid to take their time because they know that their efforts will be worth it in the end. But they are also a rogue, so their payoff is going to be efficient and lethally effective. No big flashy god move like a wizard, or loud grandstanding like bards are prone to being.

I see this character using Animal Messenger (ritual) daily to keep in contact with their spy network. Lean into this background aspect of your character and find out how much support or clout your DM will allow this group. If nothing else, they will be willing to give you information, giving you the niche of the information person. For that matter, always be observing and spying. Maybe have a notebook both in and out of character to take down information. Maybe be that mysterious person always talking to their little birds a la The Spider from Game of Thrones.

To that end I see this person using Find Familiar (ritual) because it's one of the best spying skills. You basically have a tiny drone that can fly and crawl through cracks in walls to get in places that people think are secure. If you want to cheese it the spell says you can temporarily dismiss it and then summon it again in "any unoccupied space within 30 feet of you" but it doesn't say you have to be able to see that location, so it could be .. on the other side of a wall. Now while you're looking through it's eyes you can then Misty Step there.

I see this person generally having a few summoned Unseen Servants (ritual) around with small sacks of useful items like ball bearings, caltrops, and vials of oil ready to respond to a bonus action command to deploy their tricks. A clever person will take advantage of the spell, realizing that if they give the servant an open ended or continual task, it will keep on performing that task until it is done. As an Arcane Trickster you can remain hidden and still accomplish many things since you have a main action to control your Mage Hand and a bonus action to have it do another action.

I see this person being sneaky and absolutely surgical in combat, willing to wait for a bit to really make their hits count. High intelligence characters are more likely to consider things that some people would consider "meta" like ... if I were playing this character I would pick up Hold Person at level 7 (auto crits with sneak attack? yes please) and I would absolutely say that my character has studied the effectiveness of their magic enough to know that this spell works better against targets that seem dull or unobservant (low Wisdom) and prioritize targets that way. This is backed up by the level 9 Arcane Trickster ability where their spells are more effective when they cast them from hiding.

I see this person being quiet, because they know that people confront silence by trying to fill it and exposing their secrets. That's not to say you won't be roleplaying, just that you might be doing a lot of nonverbal emoting and describing your physical actions to Intimidate, Deceive, or Persuade, for instance. Let the barbarian and the bard be loud and attract all the arrows, you'll be in the background actually getting things done.

Those are just my thoughts, of course.

Oh, a few more thoughts:

A familiar has another very relevant use. Park one on your shoulder and you will always have the ability to sneak attack in melee because there is an ally with you at all times.

Alarm is another ritual spell that can be used for clever gambits. Take an hour to set up the battle ground and you will receive advance warning of when your enemies approach, especially if your DM allows you to make each alarm bell sound different.

Daggers. I don't know why, but I see this character having lots and lots of dagger hidden all over their body.

Thank you everyone for your responses, they have all been useful.  Ophidimancer, you are spot on about my character and I've realized that I can roleplay his magic obsessions without making him a caster.  Find Familiar is what he picked for his ritual spell ( an Owl named Lore ) and Unseen Servent was not far behind.  I'm going to keep the two levels of divination wizard because if I go back to AT for the rest of my levels I dont think I will be too ******. I've also already used some abilities in the story and dont want to retcon the story.  Besides, Portent alone is amazing. 

What I'd really like to do is go back to mostly AT and tip the DM off to the fact that my character is hunting for magical items - to give him arcane versatility.  For instance when the rest of the party gets Axes of Brutal Cold Face Smashing, I would rather get 3 trinkets that come with drawbacks.  Like a glove with a charge of fireball that damages me when I use it and takes an arcana check to avoid fizzling and wasting an action. Stuff like this could really make my character feel like the one I wanted to play.

For the record our bard is a Lore Bard - this is why I feel totally overshadowed even if I made it to level 7 wiz level 3 AT.  I would just never be as good of a caster and both my player and my character hate this silly bard for being able to cast the magic I studied so hard for just with natural charisma ;)

Also I have never heard of the shadow blade spell holy **** this changes everything.

Thank you everyone, I apologize for being so ranty.  I was surprised and not proud of how annoyed I got with this problem.  I definitely do not like 5e Bards, but really I've always been a complainy butt about DnD rules - I've played too many classless systems that let me play exactly what I want.  DnD does not have that but it does have rich and detailed pre-build ideas that are very useful.

Additional Question for those still here ...

So since Im level 3 AT lvl 2 Wiz and going to focus on AT from here on out I have no access to level 2 spells and will not until level 9 ( 7 levels of AT ). I can take False life and upcast that which should help make up some of my losses, however, I could... take oooone more level of Wiz at level 6 and be 3/3 which would give me access to Shadow Blade. My thinking is that this will give me the kind of stacking damage I was after and make up for my lost AT sneak attack die for a good while until we get to higher levels. Considering I have darkness as a racial ability I can see myself using this constantly. Then all subsequent levels would be AT. Im postponing my ASI this way until level 7 but I already have 18 dex and it makes sense that my character would not be the best in the land at stealth since he is an arcane nerd as far as rogues go.   Additionally that 3rd level of wizard gives me the benefit of rounding up for arcane recovery, so for the rest of my AT life I get to recover 2 spell slots on a short rest.

If I go AT immediately and stick with only 2 wiz levels I will get my ASI at 6 *shrug* but still not be able to cast level 2 spells until 9.  I doubt we will ever get to level 20 but who knows, we arent using the Killing Stuff = XP method so its more plot milestones.  Can anyone see a good reason for me to not "complete" my dip at 3 levels of wiz down the line?

Thanks again!

What you're going to have to remember is that you're a rogue, not a mage.  Pick spells that enhance what you do as a rogue.  Movement, deception...things of that nature.  Don't rely on your magic to prop up your damage; use it to enable your rogue class features and for defense so that you're a more effective rogue.

I'd probably look at picking up booming blade and shadowblade ASAP.  Booming blade will make your single melee attack scale.  At level 5, it will be adding a straight d8 to your attack; you definitely want that cantrip in your quiver.  A tactic that can be successful, is to step up to a monster, booming blade him, bonus action -> disengage to move away.  If he moves of his own will (to you know, attack something) booming blade procs and he takes extra d8s in damage.  That's going to be useful even when shadowblade is not "up" for use (out of slots).  There's literally /no/ reason to make a single melee attack without booming blade unless you're DW.  Definitely get find familiar, your familiar can be absolutely HUGE with a rogue.  Owls for example have flyby, he can fly past your enemy, use the help action to give you advantage (sneak attack is now active) and fly out of range without provoking opportunity attacks.  Don't dip that well /too/ often or your DM will just focus on killing your familiar.  Minor illusion is also awesome.  Create an illusion of a tree, and hide behind it.  Jump out shoot something from advantage, then bonus action hide again behind your tree.

I'd probably get shadowblade sooner rather than later, but you have to remember, it's a concentration spell.  If you get hit, you may lose concentration on it.  Spell progression on AT trickster is too slow to be derping around with 1st level spells only until level 9.  Misty step is another very useful second level spell.  2nd level doesn't have a ton of offensive punch type spells, but there's a lot of utility that you can get.  Mirror image is quite nice, and not a concentration spell.  So I think I would definitely take wiz three now, even if it means delaying ASIs some more; it puts more tools into your bin.

Honestly I would say go for it and get the 3rd level of Wizard. You will be delaying your ASI for a level - but that's not a big deal - Rogues get more ASI's than normal so that will be made up for later. Getting Shadow Blade early though will really help you feel that much more powerful and the extra level will mean a little more / bigger spell slots.

If you're not going to get to level 20 then I don't see an issue. If you do get to 20 though - it would mean losing out on Elusive which is a very good ability (especially if your group plays with the flanking rules).

As an arcane trickster I kept finding that any situation in which my utility came into play - the bard has the same utility or better.

You can continue to develop your character, but I'd also talk to the DM in your situation. As a DM, I consider it part of my job to make sure every player gets a chance to be the character they want to be. When there are two utility/skill monkeys in a party, there should be situations where you both need to do something simultaneously or can only complete something by combining your efforts. The world shouldn't just sit back and wait while the characters take turns doing a single thing. You can make yourself really great for certain situations, but it's up to the DM if those situations ever turn up. Assuming they are a reasonable person, they would probably appreciate some feedback on how to make the game more enjoyable for you and potentially for everyone.

Thanks again for the comments.  It seems im definitely on the right track now.  Thank you to Emmber for pointing out Elusive - I missed that and that is. a killer ability.  However, its not worth being hobbled for the early levels considering thats where most of the playtime happens and im okay with this character being squishy.  Crzyhawk, Im ahead of you :)

Current Spell List

Cantrips : Mage Hand, Booming Blade, Minor Illusion, Thaumaturgy, Mending, Message, Light ( Thaum is from Teifling race ) 

Rituals: Unseen Servant, Floating Disk, Detect Magic, Find Familiar

Level One AT : Disguise Self, Silent Image, Feather Fall

Level One WZ: Shield, Burning Hands ( for AOE dmg, stupid swarms ), Snare, Comprehend Languages, False Life, Jump, Fog Cloud, Grease

Tiefling Spells : Darkness, Hellish Rebuke

--- Then on my next level, i get 3rd Wiz and will take Shadow Blade and ??

That last spell I have a lot of good options but im realizing how many spells compete for concentration if im trying to always use shadow blade.  Blindness / Invis / Levitate come to mind.  At least with Invis there are out of combat uses and when in combat I could use it to get into position and then see how stealthily I can get away with summoning my shadow blade without stepping on metamagic toes ( im of the opinion that AT should have a weaker subtle spell that requires a high stealth/or arcana check, ill chat with the DM about doing this. ). Pretty much the entire 2nd level wizard spell list is a treasure trove of useful utility I should be able to scribe eventually, however, Im not sure what the best pick for the level up will be.

Remember Comprehend Languages is also a ritual.  Since you have a level in wizard I would ask your DM if he can refund your Ritual Caster Feat for Skulker Feat ( Since Ritual caster is baked in with being an actual wizard).  For Second level suggestions I would look into Misty Step/Mirror Image for Defense or my favorite Dragon's Breath for your familiar for extra offence.  The Familiar has his own turn so can breath and cause damage but it does use the same concentration as your shadow blade.  

With Dragon's Breath and a bow though you can hide in the shadows with skulker and if you miss you are not revealed.  

The only positive with keeping RC is that it works off your character level so you will get the few good level 3 rituals. ( Tiny Hut, Water breathing and Phantom Steed). 

Misty step.  Most of your spell slots will be used for shadow blade, but when you /need/ misty step, you can't accept a substitute.

I'm gonna be that one voice of dissent here and say that a few wizard levels is not "Sabotaging" your Arcane Trickster.  In point of fact I've found that two to four levels of wizard interspersed throughout one's AT levels is a fantastic way to add breadth and versatility to a character that is otherwise never quite what it's trying to be.

The Arcane Trickster is a magical rogue that focuses primarily on basic rogue abilities, which it enhances with a small, select pool of subtle arcane magic.  That pool is generally too small and select; you never have the spells you want or enough slots to cast them with, and you never have enough cantrips.  Even one level of wizard gives you the same spell slot bump as three levels of Trickster; you may not have second or third-level spells to cast, but you have MOAR SLOTS(C) to cast with, and a number of classic Trickster spells upcast quite well.  If you know what you're getting into and make careful spell selections, a few wizard levels turns one's Trickster from a magic-man wannabe into a true spellblade, better than any crapass Bladesinger.

Now, the drawback is delayed access to one of the most powerful abilities in the game - Magical Ambush.  Imposing disadvantage on saves is huge.  You can partially mitigate that as a Divination wizard, using low Portent rolls to force critters to fail saves, but since you only ever get at most two of those per rest, it's something to be aware of.  Delaying Magical Ambush and Reliable Talent sucks rocks, especially as the latter is an excellent way to differentiate oneself from a skillmonkey bard.  "Oh man, that 3 was rough, buddy.  I remember when I could roll threes.  It was a bad time to be a skillmonkey.  Haven't rolled below a 10 for three levels now, but I feel ya."

'Losing' sneak attack damage is made up in part by gaining the use of combat cantrips.  Green Flame/Booming add more dice than you lose, and while yes, you can just take those as a straight AT, you didn't add magic to your rogue to spend it all on combat.  There is absolutely no reason for a Trickster not to have spells like Message, Minor Illusion, or other excellent utility cantrips.  Control Flame is a great one for rogues that do a lot of sneaky infiltration (which should bloody well be most of them); people tend to sleep on the fact that it's a purely somatic spell (no verbal component to ruin your stealth) that allows you to extinguish virtually any nonmagical light source within sixty feet of you.  Torches, lanterns, campfires?  All snuffed with a wave of your hand - and now you have a bunch of dim light or darkness to fuel your Shadow Blade!

...or, y'know, expand the flame from a torch that patrolling guard is holding five feet in the direction of the guard.  A screaming shouting ignited guard running around with his uniform on fire is a pretty intense distraction.

Anyways.  The only other thing I will note is that your tiffle racial Darkness is not going to work with Shadow Blade.  Not only is it a concentration spell (so no Darkness and Shadow Blade at the same time), but you can't see through magical Darkness with basic tiffle darkvision.  You'd be blind inside your bubble and attacking at disadvantage, which gets rid of the benefit of using Shadow Blade in darkness in the first place.  Sadly, that's a Warlock-specific combination, but fortunately you don't need it.  If you can squeeze in another cantrip somewhere, seriously consider Control Flame for eliminating light sources.  It takes an action so it's not perfectly ideal, but the sort of methodical character being described here seems to fit.

Heh.  Besides.  Just imagine the Batman moment of slowly dousing your victims' fires one by one from hiding, turning out each torch or lantern no matter how many times it's relit, driving your hapless targets just a little more wild with fear every time another light fails.

Quote from Yurei1453 >>

I'm gonna be that one voice of dissent here and say that a few wizard levels is not "Sabotaging" your Arcane Trickster...Even one level of wizard gives you the same spell slot bump as three levels of Trickster; you may not have second or third-level spells to cast, but you have MOAR SLOTS(C) to cast with, and a number of classic Trickster spells upcast quite well.

The main problem with multiclassing into another spellcasting class as an AT is that the multiclassing rules are awful for partial spellcasters. Your lose a caster level if your Arcane Trickster level isn't divisible by 3, so that first wizard level doesn't do anything for your spell slots 2/3 of the time. On the other hand 1 level in Warlock will give you access to 2-3 extra 1st level slots depending on how many short rests your party takes, twice as many if you go up to 2nd level, and many of Warlock's 1st and 2nd level features are amazing for rogues (telepathy, seeing through magical darkness, Hex, casting Disguise Self at will...)