The reader who posted the new PoE Beta Key wanted the puzzle to be a little more challenging. I didn't want to make it too lengthy or annoying though, so here you go:

__CW2 - W_M_C - HU_L_ - E6H__

To fill in the blanks, you need to answer the following riddles.

There are 2 letters per group, and nothing is jumbled up:

1st Group: You should already know this. All keys start out the same.
2nd Group: __ Red Ballons
3rd Group: Less __ More Pewpew
4th Group: The Deadmines instance is also referred to as __ because of it's boss.