Unlockable skins:
Unlock the following skins by reaching the corresponding ranks:

SKIN - RANK
Gibson (Marine) - Rank 2
Claw (Predator) - Rank 3
Warrior Dome (Alien) - Rank 4
Connor (Marine) - Rank 5
Stalker (Predator) - Rank 7
Ridged (Alien) - Rank 10
Moss (Marine) - Rank 13
Hunter (Predator) - Rank 16
Praetorian (Alien) - Rank 19
Johnson (Marine) - Rank 22
Wolf (Predator) - Rank 25
Rookie (Marine) - Rank 28
Spartan (Predator) - Rank 31
Nethead (Alien) - Rank 34