- 20 (25,000 XP)
Legendary Resistance (3/Day). If the leviathan fails a saving throw, it can choose to succeed instead.
Maneuvers. The leviathan uses maneuvers (maneuver save DC 24). It has 28 stamina dice which are d8s, a dice limit of 7, regains all expended stamina dice when it finishes a long rest and regains half its total stamina dice when it finishes a short rest, and knows the following maneuvers:
2 stamina dice: tremoring strike
Partial Freeze. If the leviathan takes 50 cold damage or more during a single turn, the leviathan partially freezes; until the end of its next turn, its speeds are reduced to 6 meters, and it makes attack rolls with disadvantage.
Siege Monster. The leviathan deals double damage to objects and structures (included in Tidal Wave).
Spellcasting. The leviathan is a 25th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 17, +9 to hit with spell attacks). It has 9 mana, a mana limit of 4, regains all expended mana when it finishes a long rest and regains half its total mana (rounded up) when it finishes a short rest, and knows the following spells:
3 mana: maelstrom
Water Form. The leviathan can enter a hostile creature’s space and stop there. It can move through a space as narrow as 2.5 centimeters wide without squeezing.
Multiattack. The leviathan makes two attacks: one with its slam and one with its tail.
Slam. Melee Weapon Attack: +16 to hit, reach 6 m. Hit: 15 (1d10 + 10) bludgeoning damage plus 5 (1d10) acid damage.
Tail. Melee Weapon Attack: +16 to hit, reach 6 m. Hit: 16 (1d12 + 10) bludgeoning damage plus 6 (1d12) acid damage.
The leviathan can take 3 legendary actions, choosing from the options below. Only one legendary option can be used at a time and only at the end of another creature’s turn. The leviathan regains spent legendary actions at the start of its turn.
Move. The leviathan moves up to its speed.
Slam (Costs 2 Actions). The leviathan makes one slam attack.