Cecaelia

Decentralized Nervous System. The cecaelia has advantage on all Intelligence, Wisdom, and Charisma saving throws.

Hold Breath. The cecaelia can hold its breath for 30 minutes.

Limited Amphibiousness. The cecaelia can breathe air and water, but it needs to be submerged at least once every 4 hours to avoid suffocating.

Regeneration.  The cecaelia regains 1 hit point at the start of its turn if it has at least 1 hit point. If the cecaelia loses a body part, the missing part regrows and returns to full functionality after 1d6 + 1 days if it has at least 1 hit point the whole time.

Underwater Camouflage. The cecaelia has advantage on Dexterity (Stealth) checks made while underwater.

Water Jet. While it is underwater, when the cecaelia moves on its turn in combat, it can double its swimming speed until the end of the turn. Once it uses this ability, the cecaelia can’t use it again until it moves 0 feet on one of its turns.

Spear. Melee or Ranged Weapon Attack: +2 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 3 (1d6) piercing damage, or 4 (1d8) piercing damage if used with two hands to make a melee attack.

Tentacles. Melee Weapon Attack: +2 to hit, reach 10 ft., one target. Hit: 5 (1d6 + 2) bludgeoning damage. If the target is a creature, it is grappled (escape DC 12). Until this grapple ends, the target is restrained, and the cecaelia can't use its tentacles on another target.