Before you hunt for special skins, understand that Prototype 2 has a default visual change tied directly to the story. This isn't a "skin" per se, but a significant alteration.
The iconic Alex Mercer skin is the ultimate reward for the RadNet service. Requirement: You must complete all 5 sets of RadNet events Conditions: how to unlock all skins in prototype 2
, which requires completing specific in-game challenges rather than just finishing the story. Prototype Wiki Alex Mercer Skin : Unlock this by completing all five sets of Before you hunt for special skins, understand that