Swellbelly

Swellbellies are large blowfish enemies that dwell in the depths of Jolly Roger's Lagoon in Banjo-Tooie It reacts to threats by puffing itself up to an enormous size, piercing anything that gets too close with the sharp spines that cover its body.

Swellbellies can be easily defeated by using the Talon Torpedo or by firing Grenade Eggs at them once Banjo and Kazooie learn how to use Sub-Aqua Egg Aim Egg Aiming underwater.

Trivia

 * Swellbellies' models are recycled directly from the Puftup enemy in Donkey Kong 64, albeit retextured. This is likely due to the games' overlapping development period.