Crab (Updated ver.)

Amphibious. The crab can breathe air and water.

Crabmatic Wrath (Recharges after a Short or Long Rest). If the crab would be reduced to 0 hit points, its current hit point total instead resets to 500 hit points, and it regains any expended uses of Legendary Resistance. Additionally, the crab can now use the options in the "Mythic Actions" section for 1 hour. Award a party an additional 10 XP (20 XP total) for defeating the crab after its Crabmatic Wrath activates.

Legendary Resistance (3/Day). If the crab fails a saving throw, it can choose to succeed instead.

Magic Resistance. The crab has advantage on saving throws against spells and other magical effects.

Multiattack. The crab can use its Frightful Presence. It then makes five attacks with its bite.

Claw. Melee Weapon Attack: +0 to hit, reach 5 ft., one target. Hit: 11 bludgeoning damage.

Frightful Presence. Each creature of the crab's choice within 120 feet of it and aware of it must succeed on a DC 17 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if the crab is within line of sight, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the crab's Frightful Presence for the next 24 hours.

The crab 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. The crab regains spent legendary actions at the start of its turn.

Attack. The crab makes one claw attack.

Move. The crab moves up to half its speed.

Chomp (Costs 2 Actions). The crab regains 30 hitpoints.

If the crab's Crabmatic Wrath trait has activated in the last hour, it can use the options below as legendary actions.

Whirlpool (Costs 2 Actions). The crab targets a creature within 5 feet of it. The creature must succeed on a DC 25 Charisma saving throw or take 44 (8d10) psychic damage and be banished to the elemental plane of water. At the start of the crab's next turn, the creature reappears in an unoccupied space within 10 feet of the aspect.

Crabmatic Flare (Costs 3 Actions). The crab flares with elemental energy. Each creature of the crab's choice in a 60-foot-radius sphere centered on it must make a DC 27 Dexterity saving throw. On a failed save, the creature takes 39 (6d12) damage of a type chosen by the crab: acid, cold, fire, lightning, or poison. On a successful save, the creature takes half as much damage.