Here is the full list of all 6 Septic Savages achievements.
Way to go! You survived 6 rounds in Arcade Mode!
You survived 12 rounds? Awesome!
18 Rounds, 3 biomes, and one champion. You rock!
Only The Void challenges you now. Congratulations!
Unthinkable! You've survived against all odds!
You've conquered the campaign! Too bad you smell now. . .