I know you can only have have 4 of one Pokémon in a deck. Does this count if you also have that Pokémon in a gx or ex form. Can I have 4 mewtwo as well as one mewtwo gx In my deck.
Short Answer, Yes.
Mewtwo and Mewtwo GX are considered different because they both have different names, despite being the same Pokemon.
Same with EX and Prisim Star cards.