Imperial Iron Wall Stops plenty of staples in the meta: , Pot of Desires Allure of Darkness Both of which are piloted by Darklords, hence they suffer a huge blow as well
Decks that deal with a lot of +1/+1 counters can still get around this effect, but otherwise, you're shutting down most creature-based strategies with this card
Mega Mewtwo Y from BREAKthrough saw significant competitive play before rotation
If that is the case such information will be made publicly known before the event, either via a news announcement or an update to that events FAQ page
It is especially significant that it can almost certainly slip past creatures with deathtouch
RB1-007 R Digimon Lv.4 Greymon Color Red Cost 5 DP 5000 Digivolve Cost 1 Red 2 from Lv.3 Form Champion Attribute Vaccine Type Dinosaur Card Text 1 [Effect] [Your Turn] While [Agumon] is in this Digimon's digivolution cards, it gains Security Attack +1