Clown College

If your adventures were a movie, you would be the comic relief. You are frequently absurdly ineffective, and the constant outrageous mishaps you experience can be exasperating to your companions.  However, you do excel at making your companions look good by comparison.  In fact, by some sort of cosmic law of balance, their performance seems to dramatically improve when they keep you around.

They might appreciate that fact and consider you a beloved mascot, or they might be oblivious to the benefits you provide and grow exasperated with you. You may be the butt of their jokes, or your antics and pun-filled remarks might be directed at another audience beyond the fourth wall.  However it happens, your ineptitude and slapstick buffoonery helps those around you to shine.

Antics

Beginning at 3rd level, your spectacularly obvious incompetence is not only exasperating, but distracting, too.  After using the Dodge action, you may use a bonus action to Help.  When you use the Help to aid a friendly creature in attacking, the target can be any creature that can see you.

Buffoonery

Also at 3rd level, whenever you succeed on an attack roll, ability check, or saving throw, you may choose to instead fail and gain one inferiority die. You may hold up to five inferiority dice at a time. On a short or long rest, all of your inferiority dice are lost.

When any creature other than you rolls a d20, you may as a reaction spend all of your inferiority dice to allow that creature to roll as many additional d20s and keep the highest result. You may never spend less than all of your inferiority dice you hold. If you are holding the maximum number, you may also spend them as a reaction to your own d20 roll.

Baneful Buffoonery

Beginning at 6th level, your buffoonery hurts enemies as well as helping allies. You may spend your inferiority dice to force your target creature to roll additional d20s and keep the lowest result.

Pratfall

The magical connection between your ineptitude and your companions' prowess reaches its peak at 14th level. 

At the start of your turn, you can use your action to expend your highest level spell slot to bolster a specified ally's spellcasting power. When you do so, you cannot use a bonus action or a reaction until the start of your next turn.  Your movement drops to 0 and you fall prone. 

If that ally casts a spell before the start of your next turn, the effects of that spell are increased, as if it were cast at a number of levels higher equal to the level of the spell slot you expended.