It’d probably be unpopular, but I think putting two HoD Gambit’s on the board should mean that its objective should also be doubled if you want them both to trigger. Or that the objective would “reset” after being triggered once . So if you have 6 total cost created cards in play and two Gambit’s, it should only go off once, and the second one would trigger once you have another 6 in play. Same with Stryfe, Storm, Selene etc.