Shadowmare

 Spellbound. Due to the magical nature of the Shadowmare, it automatically has advantage against any magical attacks directed at it.

Twilight Touched. This beast is rarely found outside the Twilight Forest, and, if outside of it, may take 2 actions to teleport itself back into the Twilight Forest, ending the encounter.

Toxic. The beast is toxic to touch, and does 1d4 poison damage per minute of contact to any target that isn't an ally. This trait also gives the beast immunity to all poisons. This trait also gives the beast's rider an immunity to poisons.

Blind. This creature is blind, and that means it cannot be blinded by a skill or spell and being blind does not give it disadvantage. However, being naturally blind means this creature's other senses are especially heightened.

Toxic Fog. (Recharge 2) The Shadowmare can expell it's toxic aura in a thick, rolling fog. This fog spreads outwards slowly up to 60ft around the creature and damages anyone in it. Dissapates after 3 turns. Every target in the mist is blinded for the 3 turns, and the fog is a Magical Area Attack: +5 to hit, 60ft circular area from self, multiple targets, Hit: 10 (2d6 +3) Poison damage per turn for each turn target fails a 13 Constitution save. The target takes half damage on a successful save.

Hooves. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage plus 7 (2d6) poison damage.

Twilight Stride. The nightmare and up to three willing creatures within 5 feet of it magically enter the Twilight Forest from the Material Plane, or vice versa.

Toxic Body. If struck in combat with bare hands or touched with bare flesh, target takes 1d4 poison damage from the Shadowmare.