I’m not quite sure whether this was intended or not, but since no such thing was ever announced I can only assume that it’s bugged. Basically the finishers have been reverting back to the billion Scarecrow or Mad King finishers (whichever was ‘used’ last from the trick-or-treat bags).
Trying to use a different finisher hasn’t worked at all for me since I’ve used either of the above to add them to the finishers collection, and it auto sets them as the currently active finisher soon as I leave the Hero’s panel, despite having changed to a different one before closing it.