Hold Breath. The optolhydra can hold its breath for 1 hour.

Multiple Heads. The optolhydra has five heads, which are a mix of eye-heads, maw-heads, and super-heads. At least one of the initial heads is a maw-head. While it has more than one eye-head, the optolhydra has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

Whenever the optolhydra takes 25 or more damage in a single turn, one of its heads dies. If all of the eye-heads die, the optolhydra is blinded until a new eye-head regrows. If all its heads die, the optolhydra dies.

At the end of its turn, it grows two heads for each of its heads that died since its last turn, unless it has taken fire damage since its last turn. The optalhydra regains 10 hit points for each head regrown in this way, or 20 hit points if it regrows a super-head. To determine what type of head regrows, roll a d12 for each new head and consult the following list:

1. Disorienting Eye-Head
2. Paralyzing Eye-Head
3. Fear Eye-Head
4. Slowing Eye-Head
5. Freezing Eye-Head
6. Stunning Eye-Head
7. Sleep Eye-Head
8. Death Eye-Head
9. Shocking Eye-Head
10. Decay Eye-Head
11. Maw-Head
12. Super-Head: counts as both an eye-head and a maw-head; roll a d10 to determine the type of eye ray it can use.

Reactive Heads. For each head the optolhydra has beyond one, it gets an extra reaction that can be used only for opportunity attacks.

Wakeful. While the optolhydra sleeps, at least one of its heads is awake.

Multiattack. The optolhydra makes as many bite attacks as it has maw-heads, and shoots as many eye rays as it has eye-heads. Each eye-head can only use its associated eye ray type.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage.

Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

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

Eye Ray. The optolhydra shoots one of the following magical eye rays at a target it can see within 120 feet of it. It must have an eye-head capable of using the eye ray in order to use it.

1. Disorienting Ray. The targeted creature must make a DC 16 Wisdom saving throw. On a failed save, the target acts as if under the effects of a confusion spell (no concentration required) for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

2. Paralyzing Ray. The targeted creature must succeed on a DC 16 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

3. Fear Ray. The targeted creature must succeed on a DC 16 Wisdom saving throw or be frightened for 1 minute. While frightened in this way, the creature takes 7 (2d6) psychic damage if it starts its turn within 30 feet of the optalhydra. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

4. Slowing Ray. The targeted creature must succeed on a DC 16 Dexterity saving throw. On a failed save, the target’s speed is halved for 1 minute. In addition, the creature can’t take reactions, and it can take either an action or a bonus action on its turn, not both. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

5. Freezing Ray. The targeted creature must make a DC 16 Constitution saving throw, taking 36 (8d8) cold damage on a failed save, or half as much damage on a successful one. A creature that fails the saving throw is also partially encased in ice and grappled (escape DC 16).

6. Stunning Ray. The targeted creature must succeed on a DC 16 Constitution saving throw or be stunned for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

7. Sleep Ray. The targeted creature must succeed on a DC 16 Wisdom saving throw or fall asleep and remain unconscious for 1 minute. The target awakens if it takes damage or another creature takes an action to wake it. This ray has no effect on constructs and undead.

8. Death Ray. The targeted creature must succeed on a DC 16 Dexterity saving throw or take 55 (10d10) necrotic damage. The target dies if the ray reduces it to 0 hit points.

9. Shocking Ray. The targeted creature must make a DC 16 Dexterity saving throw, taking 36 (8d8) lightning damage on a failed save, or half as much damage on a successful one. Up to two secondary targets, each of which must be within 30 feet of the original target, must each make a DC 16 Dexterity saving throw, taking 18 (4d8) lightning damage on a failed save, or half as much damage on a successful one.

10. Decay Ray. The targeted creature must succeed on a DC 16 Constitution saving throw or gain vulnerability to all damage until the end of the optalhydra's next turn.