Fool's Flail

Weapon (flail), rare (requires attunement)

Three jingling bells are attached to the handle of this flail, which uses 3d4 for its damage dice instead of 1d8. While holding it, you have advantage on Dexterity saving throws. In addition, whenever you roll a 1 or 20 on an attack roll made with this magic weapon, hostile creatures within 15 feet of you must succeed on a DC 15 Wisdom saving throw or be affected by the hideous laughter spell (no concentration required); this version of the spell ends at the end of your next turn.

The invaders chortled and jeered as they saw the jester cavort and twirl across the throne room, his strikes wild and witless as a drunkard in a tavern brawl. It was nigh impossible for the invaders to see him as aught else but a fool: a pathetic last line of defense for a cowering king.
Nary did they notice how each tumble put him just beyond harm's reach, nor how each mishap made the joke harder to resist—until the laughter was at last wrenched from their throats with such abandon that it drove them to their knees.
By then, it was far too late to see that the joke was on them.