Help there are 2 versions of 1 monster (2 monster cards)?

Could someone please tell me!!!

Thank You!

Note: note that I don't mean the white and red?

Right next to the picture of the monster is there a "I" or "II"? These are act one and act two of each monster. In the first half of the game you play with act one monsters and in the second half of the game you play with act II. Both are talked about in the rules.

Note, too, that the background colour is different (Act I is a grey-bluish wall, Act II is redish).