Event_Remove_Counter currently only triggers when
Duel.RemoveCounter is executed, but does not trigger when
Card.RemoveCounter is executed.
Duel removes a counter from any card on the field, whereas
Card removes only from the card itself. The actual TCG/OCG does not distinguish between these, so
Event_Remove_Counter should trigger when either occurs.
This seems to be a relic from “A” Cell Incubator, which is the only card that utilizes this event.
Of course, this has me stuck with a custom effect. Nevertheless, it doesn’t seem to be intended behavior. And plenty of TCG/OCG effects use counters, so this is bound to cause a problem at some point. Is there any chance it can be fixed/updated?