Leviathan

Eternal Caves

Hostile

Drops	Chitin (100% chance, 1-2, +1-3 with Looting); Rotten Flesh (66.7% chance, 1-2, +1-2 with Looting); Chitin Lens (33.3% chance, 1 — used to craft the Seer's Relic)
Hostility	hostile
Spawns	Swamp Cave, Lush River, Lush Cave
Strategy	Deals 8 melee damage. A large hostile mob that mainly lives in water but can walk on land, allowing it to pursue players across environments.

Movement: walk, swim, dive. Entity id panascais_caves:leviathan. Nameable. Wiki does not describe its color/shape. Health value not documented.

Sources