Poison Breath

Targets take poison damage now,
and must pass a health save, or take ongoing poison damage at the start of each of their respective turns.
The poisoning from this spell lasts until ended or treated.

Ongoing poison damage you inflict with this spell does not stack (but each caster of this spell may apply it once to the same target).
Affected creatures may spend an action to attempt a DC 13 health save to end all ongoing poison damage from this ability on themselves.

Track your ongoing damage, and remind your Headmaster about it at the start of each affected creature’s turn.

You can try a DC 15 test of Spellcraft to exclude targets in the area from being affected.