Armored Heller, Agile Armor Alex Mercer, and Zombie Alex Mercer.
If you are playing the original Prototype 2 on legacy hardware (PS3/Xbox 360) and you did not pre-order the game, you are unfortunately locked out of this method. The Armored Heller skin was originally a at GameStop and Amazon. prototype 2 how to unlock armored heller skin
Depending on where you bought the game, you might have received a code card inside the box or via email. If you bought a physical copy of the game second-hand, check the back of the manual or the inside of the case. If the previous owner didn't redeem the code, you might be in luck. Armored Heller, Agile Armor Alex Mercer, and Zombie
Shockwave, Chaos Creator Mode, and Medusa's Wrath (eyeball lasers). Troubleshooting for PC Players Agile Armor Alex Mercer