Cass' Crest is the final level of Ty the Tasmanian Tiger, taking place within Boss Cass' fortress. The bulk of the level consists of defeating swarms of Boss Cass' minions while trying to rescue Shazza from Shadow the Ghost Bat.
Once Shazza has been rescued, Ty is able to proceed to Boss Cass to foil the latter's plans. However, just before he can reach Cass' lair, Sly appears and engages him in battle during a cutscene, a battle Ty wins with incredible ease. Sly is knocked off the ledge and is about to fall into a pit of lava when Ty rescues him. Sly says that Ty will regret saving him (after having trouble finding words) and runs off, letting Ty move on to stop Cass once and for all.
Upon arrival, however, Cass is already departing in his giant robot; Ty jumps aboard, and the Final Battle ensues.