Brimstone Puffer

Spiny Body. A creature that touches the chaotic puffer or hits it with a melee attack while within 5 feet of it takes 5 (2d4) piercing damage. While the pufferfish is puffed up, this damage increases to 9 (4d4).

Scalding Water. If the chaotic puffer dies while puffed up, the boiling water within them bursts in a scalding rush and deals 16 (5d6) fire damage in a 10 ft. sphere around them.

Water Breathing. The chaotic puffer can breathe only underwater.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 15 (2d8 + 3) piercing damage, or 19 (3d10 + 3) piercing damage while puffed up.

Spine. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (2d4 + 3) piercing damage and 4 (1d6) fire damage, or 10 (3d4 + 3) piercing damage and 10 (3d6) fire damage while puffed up.

Brimstone Ignition (Recharge 6). All creatures within 10 ft. of the chaotic puffer must succeed in a DC15 Dexterity saving throw, or take 13 (4d6) fire damage and 10 (3d6) necrotic damage.

Puff Up (Recharges after a Short or Long Rest). For 1 minute, the giant pufferfish increases in size by filling its stomach with water. While puffed up, the pufferfish is Medium, makes Strength checks and Strength saving throws with advantage, and the water within them heats to a boil. If the pufferfish lacks the room to become Medium, it attains the maximum size possible in the space available.