Dullahan

• Inhuman Form. When the Dullahan suffers a critical hit from a weapon attack, they may make the creature who performed the attack reroll it, taking the new result instead. This new result cannot be altered by this effect again.
• Headless Creature. If the Dullahan ever suffers exactly 34 damage from a weapon attack, their head is destroyed. When the head is destroyed this way, the Dullahan loses the ability to see gaining disadvantage to their attacks and can no longer use their Marked for Death ability as they lose their ability to speak.
• Fey Rider. The Dullahan has the advantages of the Mounted Combatant feat. Additionally, they ride a CR1/2 Warhorse. When the Dullahan is reduced to 0 hit points, its mount disappears.

Actions

• Multiattack. The Dullahan can use its Marked For Death ability if its available, then it can also attack twice with its longsword.
• Marked For Death. The Dullahan speaks the name of the next to die at this spot. When attacking the creature who's name was spoken, the Dullahan does an additional 3d10 necrotic damage on a successful hit. This ability can only mark one target at a time and a new target cannot be chosen until the first is reduced to 0 hit points.
• Longsword. Melee Weapon Attack: +5 to hit, reach 5ft., one target. Hit 5 (1d8 + 2) slashing damage