Joint Casting

Many hands make a task easier. Many mages make a spell stronger.

While casting a spell, the caster may request assistance from any caster in the area. Both the original caster, and the ones assisting burn a spell slot equal to the spell being used. For every caster assisting with the spell, an aspect of the spell gets improved; reduced casting time by half, double duration, double damage, etc

If a caster assisting with the spell has the Joint Casting feat, two aspects can be improved

If a caster assisting with the spell can also cast the spell they are assisting with, they do not need to burn a spell slot to assist