Jack Skelington, the main character of "The Nightmare Before Christmas" was REALLY good at doing Halloween... when he tried Christmas, it was an absolute disaster. Ergo, what happens when someone with a lot of the Halloween feats tries (and fails) to take one of the Christmas feats.
Per day, per encounter... whatever works. My real point was that you needed to say per WHAT (which you seem to have added now, although perhaps I just SOMEHOW managed to miss it the first time around).
And what I am saying is that automatically causing damage, with no way to avoid or reduce it built in is USUALLY a no-no (Magic Missile being the exception). Your Pumpkin bombs seem to always hit, and not involve a reflex save for half. That didn't look right to me.