PSA : Have you or your opponent benched Teammates suddenly just drop dead on the Costume Party Monthly PF? Fear not, it's not a bug
The modifer, Trick or Treat gives out one random buff or debuff to everybody
Including benched opponents where the moment the match starts, all 6 Fighters,
Your own 3 and the opponent's 3 will get either a buff or a debuff throughout the entire match, rather than only gaining the buff/debuff only triggering once they enter the field.
One of these possible debuff is Inverse Polarity.
You can see where this is going (unless you don't know what inverse polarity does)
So if the fighter provides any form of healing to benched teammates , Inverse polarity will take affect instead, giving the good old Reverse No you, instead of healing , your fighter now take damage proportional to the healing it should have received.
This includes various cases like Flytrap SA1 and Dark lord's 100% Heal on kill (those are the only two I can think of as of writing this now)
So if suddenly your fighter or the opponent fighter drop dead while benched for whatever reason without you running a variant with "deal damage to benched opponent" while having some form of team heal available, it's not a Bug, the culprit is most likely Inverse polarity doing inverse polarity things, just that it's hard to notice since benched Fighters doesn't show whatever debuff they have