From The TimeSplitters Wiki

A glowing yellow sphere that contains a black veil. It temporarily turns the player almost invisible, leaving just a shimmering, translucent outline. With this power-up, opposition players will find it hard or even impossible to spot the user, although in TS2 bots were mostly unfooled by the effect. TS3's bots were slightly easier to trick, and they will tend to ignore the player until fired upon. Like all power-ups, it is only available in TS2 and TS3's arcade and mapmaker. One thing of note is that, in TS2, the Scourge Splitter's purple flames are still visible when he is cloaked.