Infected

Unlock Chimaira:
Mission 29: Kill one zombie by the chimaira sign.

Unlock Slipknot 0:
Mission 5: Kill one zombie by the slipknot sign.

Unlock Slipknot 1:
Mission 7: Kill one zombie by the slipknot sign.

Unlock Slipknot 2:
Mission 10: Kill one zombie by the slipknot sign.

Unlock Slipknot 3:
Mission 13: Kill one zombie by the slipknot sign.

Unlock Slipknot 4:
Mission 16: Kill one zombie by the slipknot sign.

Unlock Slipknot 5:
Mission 20: Kill one zombie by the slipknot sign.

Unlock Slipknot 6:
Mission 23: Kill one zombie by the slipknot sign.

Unlock Slipknot 7:
Mission 26: Kill one zombie by the slipknot sign.

Unlock Slipknot 8:
Mission 31: Kill one zombie by the slipknot sign.

Unlock Santa Claus or Bloodrayne:
The will be unlocked after finish all missions.