Large fey, chaotic neutral
- Armor Class 16 (natural armor)
- Hit Points 300 (30d10 + 120)
- Speed 50 ft., swim 50ft.
- Saving Throws Str +12, Wis +16, Cha +12
- Skills Athletics +6, Deception +12, Perception +9
- Damage Resistances bludgeoning, piercing and slashing from nonmagical weapons
- Senses Passive Perception 19
- Challenge 20 (25,000 XP)
- Change Appearance. The Kelpie can use an action to transform into a humanoid of its choosing. The Kelpie has advantage on all Charisma (Deception) checks while in its humanoid form.
- Legendary Resistances (3/day). If the Kelpie fails a saving throw, it can choose to succeed it instead.
- Regeneration. If the Kelpie begins its turn submerged in water, it regains 20 hit points.
- Watery Form. Whenever a melee attack hits the Kelpie, the Kelpie can use its reaction to grapple the creature using its body. While grappled this way, the creature moves with the Kelpie. A grappled creature can use an action to make a contested Strength (Athletics) check to end the grappled condition.
- Multiattack. The Kelpie can use it’s Drowning Pool then make three attacks, two with its hooves and one bite attack.
- Hoof. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 23 (4d6 + 6) bludgeoning damage. If the target is a creature, it must succeed on a DC 16 Strength saving throw or be pushed 10 feet away and knocked prone.
- Bite. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 26 (4d8 + 6) piercing damage.
- Drowning Pool. The Kelpie unleashes a whirlpool of water that pulls all creatures towards it. Any creature within 20 feet must make a DC 16 Strength saving throw or suffer 4d10 bludgeoning damage and be pulled 20 feet towards the Kelpie.
The Kelpie can take 3 Legendary Actions, choosing from the options below. Only one legendary action can be used at a time, and only at the end of another creature's turn. Spent legendary Actions are regained at the start of each turn.
- Charge. The Kelpie makes one Hoof Attack and moves 20 feet.
- Bite. The Kelpie makes one Bite Attack.
- Born of the Sea (Costs 2 Actions). The Kelpie’s body becomes entirely made of water. Until the start of the Kelpie’s next turn it gains resistance to all damage. While underwater, the Kelpie is also Invisible.