gilgamesh independent action

Servants receive certain skills when a class is attributed for the Heroic Spirit in the present world. Those skills are abilities such as Assassin's "Presence Concealment", Caster's "Territory Creation", and Saber's and Rider's "Riding". By the same way, a Servant being assigned the class Archer in the present world possesses the unique skill of "Independent Action".

This ability means he is capable of being severed from the Master supplying prana and act in autonomy; this is useful, for example, if a Master needs to concentrate all of his prana for a single large spell, or if the Master is injured and unable to supply enough prana. Yet on the other hand, it becomes harder for the Master to have the Servant accompany him and be completely under his control.

As an Archer, Gilgamesh's skill of Independent Action is ranked A. With this alone, he can use Noble Phantasms at will in battle and remain in the present world without the Master's back-up... But by having this, the King of Heroes was able to ignore Tokiomi's inclination and stroll around in Fuyuki City as he wished. Constantly apart from each other, Tokiomi can never be aware of his own Servant's whereabouts, or of what he is doing.

- Fate/Zero: Act 2, Part 4