Traveler-59 specializes in mind-control and teleportation. Their Prodigy unit is probably the most terrifying unit to face in the game, an upgraded Mastermind with the added ability to use a blink pack and utilize area of effect mind control. Cultists also can mind control units, allowing Traveler-59 to neutralize many late game threats.
Units

StalkerScrin gets a new infantry unit in the form of the Stalkers, swift moving units that fire blue tiberium shards at their enemies. They also have the ability to “Agitate Tiberium,” doing damage to any unit or structure that has Tiberium in it.

CultistsHuman bodies that have been invaded by Scrin, Cultists are able to take control of any enemy ground unit or building.

ProdigyThe Prodigy is an upgraded Mastermind that gains two new abilities in addition to the old ones – it can take control of units in a big area (temporarily), and utilize a blink pack for self-teleportation.

EradicatorThe epic unit of Scrin, the spider-like Eradicator easily crushes vehicles underfoot and collects resources from each enemy unit destroyed nearby.

Upgrades

Traveler's EnginesThis upgrade increases the speed of Traveler units. The effect can be observed on the Stalkers.

Shard LaunchersSeekers, Photon Cannons, and Plasma Disk Launchers now fire shards of Tiberium that do more damage.

Buildings
Warp ChasmThis new building is required to build the Eradicator. It can also build and repair vehicles like a normal War Factory
Support Powers
Tiberium InfestationPlaces a building on a tiberium field (much like a growth accelerator) that “infests” the field and heavily damages all enemy units foolish enough to move onto the field. Affects harvesters as well.
Temporal WormholeSlows down the speed and rate-of-fire of targeted units.
Overlord’s WrathCalls down a tiberium meteor storm to the targeted location, dealing high damage.
Other Notes
No Forcefields upgrade
No Devourer tanks