The ability to be unseen is possibly one of the best weapons and defences on the battlefield. It is an ability seldom seen (pardon the pun) naturally occurring in aliens but a mild version of this trait can be accomplished with shifting pigments in the skin, allowing chameleon-like aliens- to blend into their surroundings. Full invisibility is more commonly found in advanced technology, such as the optical camouflage developed by the Sontarans, or in ghostly, intangible creatures that barely exist in this reality.
Invisibility is a Special Trait that comes in various levels. If the ability is natural, and the user can blend into the background to be unseen, then this is a Major Good Trait. If the user remains immobile, any attempt to spot it suffers a -4 penalty.
Full optic camouflage is usually a trait that is part of a Gadget, costing 4 points. This provides the same -4 penalty to be spotted but the user can move around without losing this advantage. If this invisibility cannot be turned on or off, as in the case of the user being ethereal or immaterial, the same -4 penalty is actually a Bad Trait, providing 2 points.
All of these levels of invisibility can be purchased or taken multiple times to provide better invisibility with the penalty being cumulative. For example, if the Gadget provides almost perfect invisibility through optic camouflage, it might have the trait twice, providing a -8 penalty to anyone trying to spot the user.