Thank you for your reviews and opinions, you gave me a couple of ideas.
The elements being a permanent unlock sounds like a GREAT idea, maybe instead of cards you need to kill different elemental bosses? Maybe choosing and spawning them yourself in different zones of the map!
For the enemies I was thinking of just adding various type with different abilities but actually, just changing their stats and maybe making them spawn in unique ways is easier(like single ghosts, hordes of wolves etc), and the idea of just separating them without collisions sounds good!(they do both, mainly for the knockback that doesn't even work really well... that's probably why it's lagging) maybe I can enable collisions for the ones on screen and disable when they exit the screen, thanks for the advice!!
Also the exp make the game lag a lot, so I need to make them join and create a bigger exp when close to each other or just delete them after some time.
Again, Thank you for playing and the review!