Innate Spellcasting: Nightmare's spellcasting ability is Intelligence (spell save DC 16). Nightmare can innately cast the following spells, requiring no material components: At will: darkness, detect magic, dispel magic 1/day each: confusion, fly.
Grapple: If both of Nightmare's claws have been used to grapple creatures, it can only cast non-Somatic spells: darkness.
Multiattack. Nightmare makes four attacks: two with its claws and two with its fists. Alternatively, it makes two attacks with its claws and casts one spell, or makes two attacks with its ranged claws and has to use an action to pull them back.
Claw. Melee Weapon Attack: +4 to hit, reach 10 ft., one target. Hit: (1d6 + 5) piercing damage. If the target is a Medium or smaller creature, it is grappled (escape DC 13). Nightmare has two claws, each of which can grapple only one target
Fist. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: (1d4 + 2) bludgeoning damage.
Ranged Claw. Melee Weapon Attack: +4 to hit, reach 60/200 ft., one target. Nightmare shoots out claws to target and must use an action to retract them. Hit: (1d6+5) piercing damage. If the target is a Medium or smaller creature, it is grappled (escape DC 13). Nightmare has two claws, each of which can grapple only one target.