Wulli Wulli Oil Rig is the second boss area in Ty the Tasmanian Tiger 2. You don't actually fight a boss here though.
Ty comes here to stop a fire occurring here and from preventing Fluffy from stealing Julius' "Bio-Organic Micro Scanalyzer". After Ty confronts Fluffy, the nanobots that he followed form into Buster and he takes Ty to a boathouse area off the coast from the oil rig.
Wulli Wulli Oil Rig is in the most southern-eastern part of Southern Rivers. You can access the place via a bridge right next to South Beach, but only after Maurie tells you to go there, because there's a fence that prevents you entering beforehand. After you beat Buster, the fence is put back up and you can never access it again.