I cast Tasha’s uncontrollable farts.

You become incapacitated and you emanate a poison cloud area that damage foes and friends in a 5ft radius.

Creatures with a fart fetish get advantage on attacks towards you.

Any creature in range can use their bonus action to jar your farts and sell them on the Fart market for 2d4 silver coins each.

I can only think of two plausible interpretations of this concept.

1. Mage is broke as hell and cobbled together his own grimoire by hand-copying spells from the college library, friends, and the occasional dungeon find. Yeah, a few occult incantations slipped in there, but you’d hardly notice for all the doodles and random “todo” lists from years ago.

2. Death note.

Either way

Power word: scrunch

Casts magic missle

The sigil used for casting is just the cool S everyone drew in highschool.

I cast liquid lungs