this looks like a great start!

This is really awesome ! Even if some cards have little wording issues (like Skeletron Prime and Wall of Flesh, on top of my mind)

oh mb i'll fix them

how would you recommend changing them?

WoF : Specifiy who's end step in last ability. Skeletron : "remove an arm counter and regenerate it instead". Maw of Cthulu : "You deal damage", players never deal damage to anything. Duke Fishron, Enraged : "All abilities", technically this could imply any form of "sacrifice this creature", "this creature can't block" or Planeswalker abilities while not being a planeswalker. Golem Unleashed : The sacrifice of the head is an ability from the Head or the Golem ? Heart of Cthulu : The post-transformation ability should be rewritten to not create "copies" to word, but factual copies instead (the token has a "when this creatures transforms" when it doesn't).

The power-ups in house of hazards are quite interesting. This will increase the appeal of the game.