Cheese the Sewer Sovereign

Amphibious. Cheese can breathe air and water.

Aura of Plague. Creatures that start their turn within 30ft Cheese must make a DC 17 Constitution saving throw or gain one level of exhaustion and take 2d10 poison damage

Brutal. Cheese gets a critical success on a roll of a 18 - 20 when he attacks

Death Burst. When reduced to 0HP Cheese explodes in a shower of grime and guts. Each creature within 15ft must make a DC 17 Dexterity saving throw or take 3d6 acid damage.

Legendary Resistance 3/day. When Cheese fails a saving throw he can choose to succeed instead

Multiattack. The Sewer Sovereign can make 3 attacks when he takes the attack action .

Claw. Melee Weapon Attack: +12 to hit, reach 5 ft., 1 target. Hit: 3d8 + 7 [slashing] damage + 2d10 [poison] damage 

Siphon Life (recharge 5-6). Each enemy within 30ft of Cheese must make a DC 17 constitution saving throw or take 5d10 necrotic damage (half damage on a successful save) and Cheese regains half of that damage as HP

Children of Filth/1 day. Cheese summons 1d6 Swarms of diseased rats

Spiny Reflexes. When a creature attacks Cheese with a melee attack that creature takes 2d6 piercing as barbs along his skin flare up.

Cheese can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Cheese regains spent legendary actions at the start of his turn.

Rampage (Costs 1 Actions). Cheese moves up to half his speed and makes one attack

Noxious Miasma (Costs 2 Actions). Poisonous fumes surround Cheese in a 15ft emanation giving him half cover from all ranged attacks and any creatures within the emanation when it is created must make a DC 17 Constitution saving throw or be poisoned until the end of their next turn.