Atalas Crab

Amphibious. The atalas crab can breathe air and water

Absorbing debris. The shell of the atalas crab is coated in all manner of sea debris. Spells targeting the crab must roll a d6. On a 5 or 6, the spell targets the debris instead. The debris acts as a plant. After the debris has taken 50 HP worth of damage, it falls off, nullifying this trait, reducing the AC of the crab by 2 and activating the jagged carapace trait.

Jagged carapace. After the debris (see trait above) has fallen off, the crab's carapace is exposed which is jagged and covered in spines. Successful melee attacks done to the crab causes the attacking creature to be pierced by the spines dealing 2d6 piercing damage.

Multiattack. The crab makes 2 pincer attacks and either a crush or (if available) a sea spray attack

Pincer. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 15 (2d8 + 6) slashing damage.

Crush. The crab slams a pincer onto a target within 5 ft. of the crab. The target must make a DC 16 Dexterity saving throw or take 21 (3d10+6) bludgeoning damage.

Sea-spray (recharges on a 5-6). the crab compresses it's shell releasing a blast of water out in a 20 foot radius centered around the crab. Creatures within that radius (excluding other atalas crabs) must make a DC 16 Dexterity saving throw. On a failure, the creature takes 21 (6d6) bludgeoning damage and, if it is Huge or smaller, is pushed up to 20 feet away from the crab and knocked prone. On a success, a target takes half the bludgeoning damage, but is neither pushed nor knocked prone.

Squall. When dealt damage in excess of 35 HP in a turn, the crab may use it's reaction to release a burst of water towards the attacking creature. The creature must make a DC 12 Dexterity saving throw. On a failure the target takes 2d6 bludgeoning damage and is knocked prone. On a success the target takes half damage and is not knocked prone