A Rancor is a large carnivorous creature that can be found in the Umbaran and Felucia Combat Zones.
On Umbara, the Rancor will destroy any Droids or Umbarans it comes across and chase around the attacking player until one is defeated or the player leaves the area.
After the 13th of January 2012 Update (Original Clone Wars Adventures), defeating the Rancor would grant players pieces of the Rancor Tracking Collection which after completion would award the character the Rancor Companion “Fogg”.
On Felucia, the Rancor (Scratch) would grant you Felucia Mission Tokens which could be traded to purchase in game Gear, Consumables, or Vehicle Decorations for your Housing Lot.
The Rancor is powerful and possesses strength and endurance that takes a while to destroy, often to defeat a Rancor you would have to face them with other players.