Dullahan

Baleful Glare. When a creature that can see the eyes of the dullahan's severed head starts its turn within 30 feet of the dullahan, the dullahan can force it to make a DC 17 Wisdom saving throw if the dullahan isn't incapacitated and can see the creature. On a failed save, the creature is frightened until the start of its next turn. While frightened in this way, the creature must take the Dash action and move away from the dullahan by the safest available route. A doomed creature that fails this saving throw is restrained while frightened instead.

Relentless Advance. Moving through difficult terrain doesn't cost the dullahan extra movement, and the dullahan can move across the surface of water as if it were harmless, solid ground.

Relentless Nature. The dullahan doesn't require food, drink, or sleep.

Multiattack. The dullahan makes three Spine Whip or Necrotic Bolt attacks. It can replace one attack with a use of Seal the Doom.

Spine Whip. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 11 (2d6 + 4) slashing damage plus 10 (3d6) necrotic damage. If the target is a creature, it must succeed on a DC 17 Constitution saving throw or fall prone as it is wracked with pain.

Necrotic Bolt. Ranged Spell Attack: +7 to hit, range 120 ft., one target. Hit: 21 (4d8 + 3) necrotic damage.

Seal the Doom. The dullahan points at a creature doomed by Deathly Doom within 40 feet of it that it can see. The creature must make a DC 17 Constitution saving throw. On a failure, the target immediately drops to 0 hp if it is below half its hp maximum. On a success, the target is immune to the dullahan's Seal the Doom for the next 24 hours.

Deathly Doom. The dullahan magically dooms a creature for 1 hour. It can have only one creature doomed at a time. If it dooms another, the effect on the previous target ends. The dullahan knows the direction to the doomed creature as long as both are on the same plane of existence.