Blood-Eyed Basilisk

Bloodsense. The basilisk knows the location of any creature that has blood within 30 feet of it, provided that creature isn't behind Total Cover. Bloodsense doesn't allow the basilisk to see that creature.

Blood Eye Gaze. At the start of its turn, a creature within 30 feet of the basilisk that can see its crimson third eye must make a DC 17 Constitution saving throw. On a failed save, the creature gains one stage of crystallization.

First Failure: Crimson crystal begins spreading across the creature's body, but it suffers no additional effect.

Second Failure: The creature has the Restrained condition.

Third Failure: The creature has the Petrified condition.

A creature can avert its eyes at the start of its turn. If it does so, it can't see the basilisk until the start of its next turn and isn't affected by Blood Eye Gaze during that time. If the creature looks at the basilisk before then, it immediately becomes subject to the gaze.

Crystallization ends if the affected creature finishes a Long Rest without being Petrified or is targeted by Greater Restoration or similar magic.

The basilisk doesn't need to see a creature for Blood Eye Gaze to affect it. An Invisible creature can still be affected if it can see the Blood Eye.

Blood Eye Crystal. The basilisk's crimson third eye can be attacked separately. The Blood Eye has AC 18, 40 Hit Points, resistance to Bludgeoning, Piercing, and Slashing damage from nonmagical attacks, and immunity to Poison and Psychic damage. Damage dealt to the Blood Eye doesn't reduce the basilisk's Hit Points.

When the Blood Eye is reduced to 0 Hit Points, the basilisk takes 25 (25) Psychic damage, Crimson Beam and Crimson Glare become unavailable, and the ranges of Blood Eye Gaze and Bloodsense are reduced to 15 feet. The Blood Eye can't regain Hit Points while the basilisk is alive.

Multiattack. The basilisk makes two attacks, using Bite or Tail in any combination.

Bite. Melee Attack Roll: +9, reach 10 ft. Hit: 16 (2d10 + 5) Piercing damage plus 7 (2d6) Poison damage.

Tail. Melee Attack Roll: +9, reach 15 ft. Hit: 14 (2d8 + 5) Bludgeoning damage. If the target is Large or smaller, it must succeed on a DC 17 Strength saving throw or have the Prone condition.

Crimson Beam (Recharge 5–6). The Blood Eye fires a beam of crystallized blood in a 60-foot-long, 5-foot-wide Line. Each creature in that Line must make a DC 17 Dexterity saving throw, taking 27 (6d8) Necrotic damage on a failed save or half as much damage on a successful one.

A creature that fails the saving throw can't regain Hit Points until the start of the basilisk's next turn. The basilisk can't use Crimson Beam if its Blood Eye Crystal has been destroyed.

Petrifying Gaze (Recharge 4–6). Constitution Saving Throw: DC 12, each creature in a 30-foot Cone. If the basilisk sees its reflection within the Cone, the basilisk must make this save. First Failure: The target has the Restrained condition and repeats the save at the end of its next turn if it is still Restrained, ending the effect on itself on a success. Second Failure: The target has the Petrified condition instead of the Restrained condition.

Legendary Resistance (2/Day). If the basilisk fails a saving throw, it can choose to succeed instead.

The Blood-Eyed Basilisk can take 3 Legendary Actions, choosing from the options below. Only one Legendary Action option can be used at a time and only at the end of another creature's turn. The basilisk regains spent Legendary Actions at the start of its turn.

Skitter. The basilisk moves up to half its Speed without provoking Opportunity Attacks.

Tail Lash. The basilisk makes one Tail attack.

Crimson Glare (Costs 2 Actions). The basilisk targets one creature it can see within 60 feet. The target must succeed on a DC 17 Wisdom saving throw or have the Frightened condition until the end of its next turn. The basilisk can't use Crimson Glare if its Blood Eye Crystal has been destroyed.