Frivelgoof

Weapon (dagger), very rare (requires attunement by a bard)

Laughter is the best medicine, but an even better weapon. You gain a +2 bonus to attack and damage rolls you make with this magic weapon, which you can use as a spellcasting focus. While holding this weapon, you add your Charisma modifier to any Dexterity (Acrobatics) checks you make. 

Crowd Killer. While holding this weapon, you can cast Tasha's Hideous Laughter without expending a spell slot once per short or long rest. When you cast Tasha's Hideous Laughter while holding this weapon, the target does not gain advantage on its saving throws triggered by damage. 

Did I Do That? When you make a melee attack with this weapon, you can spend a use of your Bardic Inspiration as a bonus action to add a touch of comedic flare to your strike. If you do so, add your Bardic Inspiration die to the attack roll, which gains disadvantage. On a hit, your attack is considered a critical hit. 

Why Me? When a creature hits you with an attack, you can use your reaction to spend a use of your Bardic Inspiration to attempt to befuddle your foes. Each hostile creature within 10 feet of you must make a Charisma saving throw against your Bard spell save DC. On a failed save, a creature becomes confused by your antics and has disadvantage on the next attack roll it makes until the end of your next turn.

With each and every stumble, the fool would fall upon his face, only to be followed by yet another gout of blood from a bandit’s neck. Even as he bowed to apologize for his clumsiness his blade swung back to thoughtlessly pierce yet another raider in the throat. With each apparent blunder the gang's numbers began to dwindle; the hijinks that had previously amused them now filled them with terrible dread, even as laughter continued to spill from between their lips.

Swordtember Prompt: Jester