Twincast

Two casters are required for this spell's effect to activate.

upon casting this spell, the next damage inducing spell cast by either caster gets a bonus in damage dealt, starting at 2d10 at 2nd level, with 2 more dice added at higher levels. the effect of Twinspell cannot be given to anyone but either of the casters, and it lasts until a damage inflicting spell is cast by either of the users, or one of the casters falls unconscious, or is killed.

both users must have a spell slot equal to that of the Twincast level used, and both caster's spell slots are expended upon use. only one caster's bonus action will be taken, the one used being whoever initiates the spell.