While proliferating multiple times, players can't respond between proliferating the first time and proliferating the second time, and so on
While most cards that fulfill this purpose are supporter cards, some Pokmon have useful abilities that do this, and Armarouge is among these amazing utility cards
This can include alternate arts or even cards that are exclusively found in the Promo Packs
As well as looking the part, many of these cards fit their theme mechanically
And there you have it, the only 5 real metal Pokmon cards, meaning that all other metal Pokmon cards you encounter are fake
Factor in any other creatures that come down (like a Seasoned Dungeoneer that progresses the room on Turn 2) and it's easy to see why this mechanic is so insane