Bio-Shock. When you hit a creature with an unarmed strike using your tentacles, you can unleash a jolt of bioelectric energy. The target must make a Constitution saving throw (DC = 8 + your proficiency bonus + your Constitution modifier). On a failed save, the target has disadvantage on all Constitution ability checks for the next minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. You can use this trait a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

You have Darkvision with a range of 120 feet.

• +2 Constitution: This boosts their natural resilience and endurance, aligning with their ability to survive in harsh, semi-aquatic environments and their bioluminescent, jellyfish-like physiology.
• +1 Dexterity: Their tentacle-based movements and agility in water would make them naturally dexterous, enhancing their ability to dodge and react quickly.

Amphibious. You can breathe air and water. You gain a swimming speed 1.5x feet higher than your walking speed

Cnidarians don't have any way to communicate verbally, so Cnidarians have a natural form of communication that involves their bio-luminescence. They glow in different shades, hues, levels of brightness, to communicate ideas, thoughts, and feelings.

This bio-luminescence also sheds bright light for 10 feet, and dim light for another 5

Charge Electricity: Bio-Electric-Luminescent Surge.
As a bonus action, you can charge up your bio-electricity, preparing a burst of bright, dazzling light. On your next turn, as an action, you can release the stored energy in a 25-foot radius around you in a flash of bright light. Each creature within that radius must make a Constitution saving throw (DC = 8 + your proficiency bonus + your Constitution modifier). On a failed save, a creature is blinded until the end of its next turn. On a successful save, the creature is not blinded. A creature who already has the blinded condition automatically succeeds this saving throw.

Once you use this ability, you cannot use Bio-Shock or Bioluminescence again until you finish a short rest.

You can spend your entire turn charging to release the stored energy more gradually over time. For the next minute after that turn, all Bio-Shocks automatically succeed, causing all Constitution saving throws inflicted by Bio-Shock to automatically fail, on a number of creatures equal to your proficiency bonus. Additionally, your Bioluminescence range increases to shed 60 feet of bright light and 30 feet of dim light. At the end of this minute, you gain one level of exhaustion. You can choose to extend the length of time this state lasts, but for each additional minute spent in this state, you gain one additional level of exhaustion once the effect ends.

Once you use this ability, you cannot use Bio-Shock or Bioluminescence again until you finish a short rest.