This is a piece from MMMAJ's fanfiction, which can be found here:
http://www.fanfiction.net/u/349418/

This particular piece is from "The Four Mirrors". It shows the four Mewtwos named Nolus, Opulous, Venius, and Cygnus (from left to right.)

This picture was done by the amazingly talented Myuutsufan over on DeviantArt: http://myuutsufan.deviantart.com/ Seriously, go check out her stuff if you've ever wanted a clean Mewtwo image. (She draws risque instead of actual pr0n, otherwise she'd have a page here already.)