Black Antler Stag

Aura of Misfortune. The Stag emanates a black, misty aura in a radius of 30ft. At the start of each creatures turn, that starts its turn in the aura or moves into it must succeed on a DC 20 Wisdom Saving Throw or recieve one of the following effects: (1d4)

1. Black grease oozes from the aura which makes the area difficult terrain. In addition, whenever a creature makes a weapon attack within the aura, it must succeed on a strength saving throw or drop his weapon. 
2. Thick smoke fills the area, covering the air with dense black particles. The area becomes magical darkness. Additionally each creature in the area must succeed on a DC 20 Int saving throw or be subjected to the Phantasmal Force as past failures glow up in the darkness.
3. Draining energies from the negative energy plane drain away vitality. In the area, no life points can be restored. Additionally, each creature takes 3d6 necrotic damage.
4. A mirage of pictures presents the greatest follies of all history, draining magic and elemental energies. The Area becomes an anti-magic field. In addition, each creature becomes immune to fire, cold, acid, lightning and thunder damage. 

At the end of each of the Stags turn, the effect is rerolled. 

Magic Resistance. The Stag has advantage on saving throws against spells and spell effects.

Multiattack. The stag makes 3 attacks. 

Gore. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 2 (3d10+8) piercing damage.

Hooves. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 2 (2d12) bludgeoning damage.

Charge. If the Stag moves at least 20ft he can make a Gore attack as a bonus action.