Defeat 100 monsters in Skeleton Form

Complete stages 5 to 8

Kill 50 Chimera by detonating their heatstacks in the Single Player Campaign

Kill Gorrell

Kill 50 Chimera with Riley's axe in the Single Player Campaign

Kill 1000 Chimera in the Single Player Campaign

Upgrade all weapons in the Single Player Campaign

Kill an enemy with every weapon in the Single Player Campaign

Kill an Impaler

Kill 500 Chimera in the Single Player Campaign

Successfully complete level 2

Kill 250 Chimera in the Single Player Campaign