Run, stalker, run!

The Chimera is a rare spawn only in certain locations - see the linked map and search for Chimera. The Chimera is fast, can jump a long way, and can knock you down easily. Bring an energy drink. As soon as you spot one, run away as fast as you can and the achievement should pop once you've escaped.

NB its possible (not confirmed yet) that taking damage can invalidate the achievement - try not to get hurt!