Poison vulnerability cone- for the range of a 100 ft cone creature have a poison vulnerability, and have the lose all resistances or immunities to poison damage and the poisoned condition.

Bite. Melee Weapon Attack: +1 to hit, reach 5 ft., one target. Hit: 2 (1d6 − 1) piercing damage.

Eye Rays. The yuan ti spectator shoots up to two of the following magical eye rays at one or two creatures it can see within 120 feet of it. It can use each ray only once on a turn.

1. Confusion Ray. The target must succeed on a DC 13 Wisdom saving throw, or it can’t take reactions until the end of its next turn. On its turn, the target can’t move, and it uses its action to make a melee or ranged attack against a randomly determined creature within range. If the target can’t attack, it does nothing on its turn.
2. Paralyzing Ray. The target must succeed on a DC 13 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 target must succeed on a DC 13 Wisdom saving throw or be frightened for 1 minute. The target can repeat the saving throw at the end of each of its turns, with disadvantage if the spectator is visible to the target, ending the effect on itself on a success.
4. Wounding Ray. The target must make a DC 15 Constitution saving throw, taking 32 (6d10) Poison damage on a failed save, or half as much damage on a successful one.
5. Poison Ray.  The target must make a DC 15 Constitution saving throw, or be poisoned for 10 minutes.
6. Exhausting Ray. the target must make a DC 15 Constitution save or have gain one level of exhaustion.

Create Food and Water. The yuan ti spectator magically creates enough food and water to sustain itself for 24 hours.

Spell Reflection. If the yuan ti spectator makes a successful saving throw against a spell, or a spell attack misses it, the spectator can choose another creature (including the spellcaster) it can see within 60 feet of it. The spell targets the chosen creature instead of the spectator. If the spell forced a saving throw, the chosen creature makes its own save. If the spell was an attack, the attack roll is rerolled against the chosen creature.

The yuan ti spectator can make 3 legendary actions

Eye Ray. The Yuan Ti Spectator makes one randomly determined eye ray attack