You may use a bonus action to honk the horn. When honked the player may roll once on the wild magic table. 

Curse. Once attuned to this item, you cannot be unattuned from it or remove it from your inventory unless the remove curse is used. When rolling a 1 on an ability check, saving throw, or attack roll, the horn will honk as if the player had honked it. This requires the player to roll on the wild magic table. This does not use a charge.

Wielded by Snow the Clown, the abyssal clown horn appears to be a simple horn with a red rubber hollow ball on one end that when squeezed, forces air through the horn. When the horn is honked, abyssal alphabetic characters appear on the metallic body of the horn. 

Notes: telling a joke of some kind, and then honk the horn. The item cannot be attuned to in this way until the next dawn., Cursed, Instrument, Bard