These stormtroopers wore an experimental armor developed by the Galactic Empire which mixed elements of advanced survival gear as well as the ability to absorb energy discharges with that of a personal cloaking device. This made them extremely rare, though they were often sent on operations on alien worlds which involved menacing the local inhabitants and assassinating resistance leaders.
Similar to the shadow troopers, they were often called into battle by stormtrooper commanders where they used their cloaking devices to ambush their enemies where they opened a barrage of fire from their deadly FA-3 flechette launchers.
The only known usages of shadow EVO troopers were in 2 BBY, when several were posted with the Imperial garrison at the Jedi Temple, at Raxus Prime's ore collection facility, and on the unfinished Death Star I. They came into conflict with Galen Marek several times, and were repeatedly defeated by the Dark Jedi. Also they were used on Raxus Prime to assist the EVO troopers.
Starkiller also encountered them as they were guarding the Jedi Temple when he infiltrated for his Trial of the Spirit.
- The Complete Star Wars Encyclopedia