College of Humor

Lore: Jokers, jesters, wise guys, and crack-ups. These bards use their talent for the various forms of comedy to fool and confuse their enemies.

3rd Level: The Power of Laughter
You learn the "Vicious Mockery" cantrip (If you already know "Vicious Mockery" pick any other Bard cantrip). The damage dice of "Vicious Mockery" becomes equal to your Bardic Inspiration dice. Finally, when an enemy is attacked you may use your Reaction to roll a Bardic Inspiration die, reducing the targets Armor Class by the rolled amount.

6th Level: Prat Fall
You become immune to being knocked prone.

Also when falling if you are within 5ft of a wall you may use your Reaction and roll a Bardic Inspiration. Reduce the damage you take by the amount rolled x 5.

14th Level: Killing Joke
When casting a spell of the Enchantment or Illusion schools, increase your Spell Save DC by 2.

You may use your Action to force an enemy within 30ft to make a Charisma Saving Throw (DC 8+Proficiency+Charisma+2). On a Failed save the target immediately drops to 0 and on a Successful save the target instead falls prone, their speed drops to 0, and they have disadvantage on Dexterity saving throws. This effect lasts up to 1 minute. The target must share one language with the Bard and have an Intelligence above 4 or they are immune to this effect. This recharges on a Long Rest.

Quote from BustyRusty1 >>

College of Humor

Lore: Jokers, jesters, wise guys, and crack-ups. These bards use their talent for the various forms of comedy to fool and confuse their enemies.

 Hi BustyRusty1 o/

I can't help but immediately think of The Joker, when reading this, not sure why (maybe for Killing Joke).
The sublcass idea is real good, but I have a couple of feedback:

 3rd Level: The Power of Laughter
You learn the "Vicious Mockery" cantrip (If you already know "Vicious Mockery" pick any other Bard cantrip). The damage dice of "Vicious Mockery" becomes equal to your Bardic Inspiration dice. Finally, when an enemy is attacked you may use your Reaction to roll a Bardic Inspiration die, reducing the targets Armor Class by the rolled amount.

This is quite powerful, but I think it is also balanced enough for the Vicious Mockery part. I am not sure the second part is really balanced, but needing to sacrifice a BI dice might be enough.

 6th Level: Prat Fall
You become immune to being knocked prone.
Also when falling if you are within 5ft of a wall you may use your Reaction and roll a Bardic Inspiration. Reduce the damage you take by the amount rolled x 5.

Immunity to conditions, and one so hindering as Prone is quite powerful, especially at a low-ish level like 6th.
I would suggest to change it to something like: whenever you would become prone due to an effect or attack, if you still have at least 5 feet of movement available in this round, you can instead move 5 feet away from the source of the effect or attack; this movement could still provoke attacks of opportunity.

 14th Level: Killing Joke
When casting a spell of the Enchantment or Illusion schools, increase your Spell Save DC by 2.
You may use your Action to force an enemy within 30ft to make a Charisma Saving Throw (DC 8+Proficiency+Charisma+2). On a Failed save the target immediately drops to 0 and on a Successful save the target instead falls prone, their speed drops to 0, and they have disadvantage on Dexterity saving throws. This effect lasts up to 1 minute. The target must share one language with the Bard and have an Intelligence above 4 or they are immune to this effect. This recharges on a Long Rest.

This is good, but a couple of notes: the "+2" to the save DC seems weird, and would not shift the chances of success/failure too much, so I'd probably take it out; just nitpicking, but I think there's a missing "HP" in "On a Failed save the target immediately drops to 0 and"; there is also no specific indication of how many times this can be used, but only the recharge. I assume it's once every long rest, but it's always best to specify these sort of things, imho :)

Overall, good job!!

For The Power of Laughter, I assume you have to expend a bardic inspiration.

Prat Fall. I have to agree with LeK on this one. Perhaps you have advantage against being knocked prone?

I'm worried about Killing Joke. Look at power word kill. This is a 9th spell that does nearly the same thing. Many DMs will rule that once an enemy is at 0 hit points, it's dead. Perhaps halve their current hit points?

Instead of a +2 to the DC what about targets getting disadvantage on your enchantment and illusion spells?

I think it can be balanced on the 0HP thing, looking at Quivering Palm from the Open Hand Monk.

QP is triggered on a melee hit, and even though CON saves can be, on average, higher than CHA saves, I think the 10d10 damage QP does on a successful save is quite more powerful than the effects of Killing Joke in that case. KJ is 3 levels lower than QP, but QP has no distance/time requirements, making extremely powerful and tactical; KJ has a 30feet range and instant effect, so it sounds balanced to me if properly limited in the amount of uses.

Quote from LeK >>

I think it can be balanced on the 0HP thing, looking at Quivering Palm from the Open Hand Monk.

QP is triggered on a melee hit, and even though CON saves can be, on average, higher than CHA saves, I think the 10d10 damage QP does on a successful save is quite more powerful than the effects of Killing Joke in that case. KJ is 3 levels lower than QP, but QP has no distance/time requirements, making extremely powerful and tactical; KJ has a 30feet range and instant effect, so it sounds balanced to me if properly limited in the amount of uses.

 Quivering palm is introduced at 17th level, spellcasters have 9th level spells. At 14th level, spellcasters can only cast 7th level spells. The abilities are also introduced in different tiers of play. I worry that other players might feel over shadowed as the bard can cast the equivalent of a 9th level spell at 14th level. I can totally see the subclass working the way it is, but I would handle this feature with caution.