You know, I don't think it's as intended, but isn't large creatures weapons dealing more damage actually a rule? Meaning that a longsword with this should technically still deal 2d8+1d4 even though it doesn't say anything about adding to the weapon die. Am I wrong? Is it not actually specifically stated in the rules that large weapons automatically double their amount of damage dice?

Quote from ShaydyCharacter >>

You know, I don't think it's as intended, but isn't large creatures weapons dealing more damage actually a rule? Meaning that a longsword with this should technically still deal 2d8+1d4 even though it doesn't say anything about adding to the weapon die. Am I wrong? Is it not actually specifically stated in the rules that large weapons automatically double their amount of damage dice?

 It is one of many instances where there are multiple rule effects for the same thing in-game.  WotC really just needs to get its designers together & decide "This is what happens when you are Large/Huge/Gargantuan." and apply that consistently.

I know this is super late, but you could always have it use a spell slot of a higher level to reduce the size smaller.

Quote from ShaydyCharacter >>

You know, I don't think it's as intended, but isn't large creatures weapons dealing more damage actually a rule? Meaning that a longsword with this should technically still deal 2d8+1d4 even though it doesn't say anything about adding to the weapon die. Am I wrong? Is it not actually specifically stated in the rules that large weapons automatically double their amount of damage dice?

 This is how it works. The rules are in a weird spot, sure, and many people like to do mental gymnastics to say they don't make sense, but they ARE rules for large weapons, not just making a monster.

When people point out THIS spell and go "but Enlarge/Reduce only gives you a D4!"

THIS SPELL DOESN'T MAKE YOU LARGE. IT INCREASES YOUR SIZE BY ONE STEP. A small PC, such as a halfling, would become medium. You STILL get a d4 because of the spell. A medium PC, such as a half orc, would become large, and thus get a d4 from the spell and an extra weapon die from having a large weapon.

4d6+1d4+mod sounds like a lot, but being large also has drawbacks. A medium creature needs 2 or 4 creatures to flank it, but a large creature can be flanked by 3 (2 on one side, one on the opposite side) so it IS technically easier to get flanked. Cover just big enough for a medium creature doesn't cover a large creature. Covering more space means you can be included in AoEs easier. A spell like Lightning Bolt, basically fireball in a line, might have missed you when lining up with another target, but being chunky put you in its path.

And what if someome takes your weapon? Or just makes you drop it? It loses its extra size, and probably doesn't come back under the effects of the spell when you pick it back up.

That ruling gets really wild if you stack rune knight's giant's might and this spell which makes your size huge.  Then with a great sword you are dealing 6d6 from a huge weapon + 1d6 from giant's might + 1d4 from enlarge + strength modifier.  Then at 18th level you can basically do this with  just giants might which becomes runic juggernaut  and enlarge can then make you become gargantuan to  do even more. At gargantuan that's 8d6 from a gargantuan great sword + 1d10 from runic juggernaut + 1d4 from enlarge + strength. You literally hit  harder than a fire ball 4 times a round and don't even get me started on action surge. 

Personally I love the idea of fighter kaiju just be aware that this can happen 

It gets wacky, sure, but it does have drawbacks. And you NEED the space to become large or bigger.

9th level spells get to do a ton of damage. Meteor swarm is 40d6, and you get FOUR 40ft radius spheres, so that's just battlefield obliteration. Granted, you can't stack the meteors on one guy, but your AoE ability has a ton of room to catch a lot of people. Blade of Disaster is 4d12, critically striking on 18-20 for 12d12... attacks twice a round, as a bonus action.

If you COULDN'T do more damage while large, a fighter attacking with a greataxe could deal only 3d12 plus 15 by the time a caster gets Blade of Disaster. Then, FINALLY, at level 20, a fighter can do 4d12 plus 20.

The only reason to keep martial classes from doing more damage is "but muh wizzzerd! He control space/time and all da elemunts! No way a guy with a sword can do stuff in combat!" Which is just prejudiced gatekeeping. I see that argument a lot. "I can control the very elements! MY wizard is do POWERFUL!" but like... are they? My friend's dm blocked the group from loot by saying their 1st level spell, burning hands, completely incinerated the whole body and everything it was wearing. And I'm just like... burning hands does 3d6, or 3d8, something like that. Can completely incinerate flesh bone and metal, but like... a horse, with more max hp than the spell has damage, would still exist. The TOUGHEST Barbarian would have 380 hp. Meteor Swarm, rolling max damage, would only do 240 damage. Your average fighter would max out at about 224 hp, provided they maxed constitution. An average damage roll would only do 140 damage. So, like... I don't think magic or spellcasters are as amazing as people like to say. You can bend reality a little bit by making flames spontaneously appear, sure, but you're not REALLY master of the universe.

So, all in all, just let the gargantuan fighter do gargantuan sized damage. If they combo that hard, if they've worked that hard to be level 18 to 20 to be powerful, they've earned it at the very least. And it's still only single target damage. No matter how much damage they can potentially do, they can still only kill 4 goblins per turn... or 8, with action surge. 

Anyway, I kinda hope this helps anyone reading this. I know some people out there fear letting anything have more power, but it's okay. 3d12 an attack isn't going to break your game at level 3, the earliest a rune knight and a wizard can combo. The fighter only has 1 attack at that point. Most likely doesn't even have 20 strength yet. Had to use 2 buffs (one of which is concentration, so bully that wizard!) to even get there. If they get REALLY lucky, they can do 50 damage to your boss monster, sure. But that's max damage on all dice. They can also get really unlucky and only do 9 damage. And the fighter probably has less than 30 max hp. They're still in danger. Don't be intimidated by your player's power combos, just play the game.

Can you use this to abuse ranger beast companions? Say lvl 3 you find a large beast like a dire wolf, you reduce it to a medium size, choose it as your animal companion, then later when spell wears off you now have a large animal companion?

Quote from Alburan >>

Important question: can this spell be used in conjunction with other spells? Such as wall of stone? 

 This spell requires concentration, so you would need another spellcaster.  But a wall of stone is an object, so yes.  You can grow it.    

"If the target is a creature, everything it is wearing and carrying changes size with it."

So let me get this straight... if the creature is mounted like a horse and a rider, does rider grow too? Their weapons aren't the target's weapons so they don't get extra damage, but this would make for a really cool flavoring of a drakewarden flying around with extra size no? ^^

"Any item dropped by an affected creature returns to normal size at once."

Since a rider would be a person instead of an item, would they retain the size change if they got it?

Would your dm consider the mount to be wearing or CARRYING you its up to your dm but rules as written yes its carrying you keep in mind it also means that you would instantly shrink if you fell off the mount

bugbears are large tho

Also for Duregar.

RAW this can be used to shrink doors and gates to allow passage through!

To be fair, Rune Knight dip will allow character to grow up to Large from claasfeat and then to Huge with this spell. Not Gargantuan though.

Ranger could really do with a version of this for Animal companions, familiars, and beasts.
Enlarge beast but as a bonus action which increases damage and duration at higher spell slots would really keep your companions in the game. You wouldn't even need to be a beastmaster to find use. Just find a friendly bear with a shared enemy and watch him go

Looking forward to this being cast on a Path of the giant Barbarian

What would happen if this was cast on an already Gargantuan target?

Also how does this interact with the Blistercoil Weird’s ability that makes it grow and get stronger when it takes Fire damage?

Quote from Solarsyphon >>

That ruling gets really wild if you stack rune knight's giant's might and this spell which makes your size huge.  Then with a great sword you are dealing 6d6 from a huge weapon + 1d6 from giant's might + 1d4 from enlarge + strength modifier.  Then at 18th level you can basically do this with  just giants might which becomes runic juggernaut  and enlarge can then make you become gargantuan to  do even more. At gargantuan that's 8d6 from a gargantuan great sword + 1d10 from runic juggernaut + 1d4 from enlarge + strength. You literally hit  harder than a fire ball 4 times a round and don't even get me started on action surge. 

Personally I love the idea of fighter kaiju just be aware that this can happen 

The Antimatter Rifle included as a futuristic weapon in the DMG does 8d6 damage by default. It normally can only shoot 2 shots before needing to be reloaded with Energy Cells, which you will probably have a limited supply of if your DM even lets you have an Antimatter Rifle, but Repeating Shot from an Artificer can supply infinite ammo, as well as a +1 on attack and damage rolls.

That is 32d6 + 1d10 + 1d4 + 6 Necrotic damage with maximum DEX, or an average of 126 damage per attack. Multiply that by 8 for Action Surge, and you get 1,008 Necrotic damage per round with no extra buffs.

That kills basically anything without Necrotic resistance or immunity in one round, and will likely kill most enemies with resistance anyway. 

On average, it kills Vecna the Archlich in 5 shots, or a Tarrasque in 6.

It takes down both The Aspect of Tiamat and The Aspect of Bahamut in 2 rounds. 

The only super high CR enemy I can think of that could reasonably stand up to a party using this is a Topaz Greatwyrm, due to it’s Necrotic Damage immunity. 

Quote from Panzerov >>

RAW says one can not be affected by two spells or effects with the same name. Homebrew says you can do whatever you feel like though :)

 This lasts until you get a friend to cast Geas on you to always blink regularly, thus making you immune to any less pleasant Geas spell and the DM gives you the stinkeye.