If you play as a gnome, and cast reduce on yourself, you will weigh less than 5 pounds on average. This means that you can grab yourself using mage hand to fly. As ridiculous as it sounds, it actually checks out with the spell description, as well as the player's handbook. 

The cheaper option is to use Unseen Servant, which has a Strength Score of 2, translating to a carrying capacity of 30lbs. Kobolds generally range from 25~35lbs.

The other controversial option is to use Mage Hand to push a target suspended by Levitate. If Levitate makes the target weightless, then it should be easy to do, however, that would imply a lot of unaddressed issues.

RAW, a dragonborns breath weapon works whilst wildshaped, meaning you can become a fie-breathing squirrel.

But mage hand can only be used to manipulate objects (not creatures).

Can an Dragonborn artificer use their Repeating Ammunition trait to infinitely use Breath Weapon? Just curious.

If you cast gate or a similar spell inside or on a Bag of Holding, you can pretty much make it into a bomb that sucks everything around it into the Astral Plane. Given that these are uncommon magic items, you can probably buy loads of these at higher levels. This tactic is stupidly overpowered as there isn't even a saving throw: If you're close to the bag, you're pretty much dead.

You can use Dimension Door or Etherealness to skip an entire dungeon. This is an absurd and hilarious tactic you can use to drive the DM nuts.

Summon Lesser Devils or using a similar spell lets you make, I kid you not, 16 attacks per round. This is a 3rd level spell that can deal over 70 damage.

Quote from ThorukDuckSlayer >>

RAW, a dragonborns breath weapon works whilst wildshaped, meaning you can become a fie-breathing squirrel.

 You can also Rage while wild shaped, AND use martial arts!

Quote from SpiderQueenYvonne >>

If you cast gate or a similar spell inside or on a Bag of Holding, you can pretty much make it into a bomb that sucks everything around it into the Astral Plane. Given that these are uncommon magic items, you can probably buy loads of these at higher levels. This tactic is stupidly overpowered as there isn't even a saving throw: If you're close to the bag, you're pretty much dead.

 
I don't get the "dead" part. It doesn't cause damage, it just sends you to the astral plane which is generally safer than the material and you can find any portal back by just heading in any direction for less than 2 days.

It's a useful tactic I suppose, but seems like a very expensive version of plane shift.

Quote from SpiderQueenYvonne >>

Can an Dragonborn artificer use their Repeating Ammunition trait to infinitely use Breath Weapon? Just curious.

 No, Repeating Ammunition is an infusion, and your breath is not an item (If your breath becomes an item, ask your dm)

According to Storm King's Thunder, a medium creature can wield a giant sized dagger. It counts as a greatsword that deals 3d4 + Str on a hit.

If a DM uses the Law of Averages variant rule during a campaign set in Mechanus, without using homebrew, the lowest damage that would be impossible to deal with a single attack  from any non-buffed / non-weakened creature would be 38.

The CR calculation method in the DMG often produces quite different results to the CR's given to creatures by WotC. The biggest difference between a CR calculated by the DMG and the CR given by WotC for a creature from the Monster Manual is the Rakshasa, the DMG gives a CR of 6, a difference of 7. The most likely reason for this difference is the lack of a way to factor in the Rakshasa's Magic Immunity, Dominate Person or the curse in its claws into the DMG calculation method.

If you get the Rod of Security, you can use it to live forever. I kid you not! Time passes like it does in the Material Plane in the demiplane you create, but you don't age. Since the demiplane lasts for up to 200 days (depending on the amount of people in the demiplane), you can EASILY cast it again before the duration runs out. Magic can't be used to find you while you're in the demiplane, so any world-ending monsters the DM punishes you with can't even reach you. And that is how you become truly immortal in D&D*.

*Yes, I know liches are a thing, but you can still die as a lich, so it technically isn't immortality. True immortality means you cannot die by any means, not just by aging. Liches, despite their rejuvinating abilities, can still be hurt and die. This goes double if their psylacteracy is destroyed.

Quote from SpiderQueenYvonne >>

If you get the Rod of Security, you can use it to live forever. I kid you not! Time passes like it does in the Material Plane in the demiplane you create, but you don't age. Since the demiplane lasts for up to 200 days (depending on the amount of people in the demiplane), you can EASILY cast it again before the duration runs out. Magic can't be used to find you while you're in the demiplane, so any world-ending monsters the DM punishes you with can't even reach you. And that is how you become truly immortal in D&D*.

 

*Yes, I know liches are a thing, but you can still die as a lich, so it technically isn't immortality. True immortality means you cannot die by any means, not just by aging. Liches, despite their rejuvinating abilities, can still be hurt and die. This goes double if their psylacteracy is destroyed.

 
Slight issue: the 10 day recharge doesn't begin until you have left the created demiplane. 

And Divine Smite....

Do not fear, as I have a solution. Just chuck the Rod of Security outside of the demiplane, and use mage hand or unseen servant to bring it back in. Since it left the demiplane, its 10 day cooldown is activated, and you don't even have to leave the demiplane!

Quote from SpiderQueenYvonne >>

If you play as a gnome, and cast reduce on yourself, you will weigh less than 5 pounds on average. This means that you can grab yourself using mage hand to fly. As ridiculous as it sounds, it actually checks out with the spell description, as well as the player's handbook. 

 But for that same 3rd level spell slot, you can cast fly.

Quote from SpiderQueenYvonne >>

Do not fear, as I have a solution. Just chuck the Rod of Security outside of the demiplane, and use mage hand or unseen servant to bring it back in. Since it left the demiplane, its 10 day cooldown is activated, and you don't even have to leave the demiplane!

 
Again, not possible, there is no doorway you can step through. You are transported into the plane, you don't pass any doorway. And the only two ways to leave is to wait for the time to run out or use an action to end the effect and in either case everyone is transported back. 

Perhaps a banish* is in order, then. banish is one of the few location-changing spells that has a duration. This means you can send the Rod of Security somewhere to some other plane, starting its 10 day cooldown. Then, when the spell wears off, it shows up back in the demiplane! While magic can't be used to find your demiplane, it can be used to reach it. This means the Rod of Security should have no trouble finding its way back!

*Yes, I know banish is a 6th-level spell (or at least, that's what I think it is), but even if you aren't a expert spell caster, fear not! There's a multitude of ways to gain XP in downtime, like training, studying, and exercise. Given that you have 200 days in the demiplane, you can essentially treat some of that time as a reeeeeaaally long training montage. This gives you the levels needed to cast banish, and then some!

Quote from Cyb3rM1nd >>

Quote from SpiderQueenYvonne >>

If you cast gate or a similar spell inside or on a Bag of Holding, you can pretty much make it into a bomb that sucks everything around it into the Astral Plane. Given that these are uncommon magic items, you can probably buy loads of these at higher levels. This tactic is stupidly overpowered as there isn't even a saving throw: If you're close to the bag, you're pretty much dead.

 
I don't get the "dead" part. It doesn't cause damage, it just sends you to the astral plane which is generally safer than the material and you can find any portal back by just heading in any direction for less than 2 days.

It's a useful tactic I suppose, but seems like a very expensive version of plane shift.

 Given the fact that the Astral Plane is often interpreted as one of the 'afterlife destinations', they could technically be counted as dead in a certain sense. This goes double if whatever you banished was unfortunate enough to come across one of the numerous monsters in there. Githyanki airships swarm the Astral Plane, so there's a god chance that your target will bump into one on their 2 day trek.