So, let's say the player never mentioned anything of the card, just had it lying there. Still Game Loss?
Now, say it's a SF Lumineon (players could try to empty azelf/uxies from hand) Still a game loss?
Now let's say it's a Bidoof, still a game loss?
If the player says nothing and just has that card in their deck or in play, they're legal.
I think I've said that.
The problem is the instant that they make any misleading statement.
As I've said before, since people seem to not "get" the distinction between legal and non-legal, this is really something people should stay away from.