The final boss of the Mermalair is Prawn. After SpongeBob shuts down the security system, Prawn is released from the Villain Containment System. Prawn is surrounded by disco tiles that flash rapidly. The fight consists of dodging his sonic waves and Ham-Mer robots. After Prawn's attacks finish, the disco floor reveals a lane to shoot a bubble bowl. Prawn takes 3 hits to defeat.
Out of bounds directly above the spawn, an invisible debug trigger exists. Touching this invisible trigger causes the fight to instantly complete. After the cutscene finished, the player is teleported back in-bounds on all platforms except for GameCube.
With a precise bowl, the player can clip out-of-bounds without a Cruise Boost. The player can reach the trigger in multiple ways, either from the top with a bowl ledge jump, or from below, by bashing off the top of the bubble bowl.