Levels are not replayable, stats do not stack from game to game.
ROCK OF AGES
This can be gotton by throwing all items conan can pick up, except weapons. I mean boulders, crates, vases, etc.
I just got it in the midnight raid level after crushing a captain with a crate.
A trick to this achievment is to turn on the infinite armor power and stone skin the enemies, then one rock/crate/vase will kill them.