Successfully complete level 4

Kill an enemy with every weapon in the Single Player Campaign

Kill 500 Chimera in the Single Player Campaign

Kill an Impaler

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

Kill the Abomination

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

Successfully complete level 1

Upgrade a weapon in the Single Player Campaign

Defeat all enemy waves in the Gates of Hell Arena

Complete the Dark Forest on any difficulty

Reach Unholy Level 7