Counterparts

So this is Copycat's Halloween skin.

The left demon-based one is the actual skin that'll be used, while the angel one is just what her double looks like when using her Double Trouble ability.
It's supposed to be metaphorical, but eh.

The suits were made by Overwatch (as guessed.), but she just sharpied the ANG3L and D3M0N on herself, in-case her costume wasn't obvious enough.

Possible Interaction

Mercy: Your costume looks great this year, Lauren!
Copycat (Demon skin needed): Aww, you're makin' me blush...but, I will never be as good as the original, hm?

Also, yes.
The wings are literally things she bought at the local Dollar Store.