it's obtainable, just tricky to get.
look out for sources of smoke in the caves ^^.
Is it a ways in the level, do I have to bounce across those platforms or is it in in a secret wall. Cause I found several of those crystal things in the walls and this one is eluding me. A general clue will be good... unless I find it before you next respond. Do you really have to kill every enemy without dying to get that? I have a feeling I have them all