Incorporeal Movement. The Yunstreiter can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Blurred Form. Attack rolls against the Yunstreiter are made with disadvantage unless it is incapacitated

Magic Resistance. The Yunstreiter has advantage on saving throws against spells and other magical effects.

Spellcasting. The Yunstreiter can cast the following spells, requiring no spell components and using Charisma as the spellcasting ability (spell save DC 18):

3/Day Each: fear, hunger of hadar, raise dead

1/Day Each: circle of death, harm

 Multiattack. The Yunstreiter makes two melee attacks or uses its Bile. 

Cursed Slam. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 20 (4d8+4) necrotic damage. It the target is a creature and is not undead, the Yunstreiter gains hit points equal to the necrotic damage dealt.

Bile (Corpse Form Only). The Yunstreiter forces its host to spew bile in a 15 foot cone. Creatures in the cone must succeed on a DC 16 Dexterity saving throw or be covered in bile until a creature uses its action to scrape or wash the bile off itself or another creature. A creature covered in the acid takes 19 (3d6) acid damage plus 7.

Corpse Jump. The Yunstreiter disappears into an undead humanoid within 30 feet of it that the Yunstreiter has raised. The Yunstreiter is immune to bludgeoning, piercing and slashing damage while inside the undead. The Yunstreiter is undetectable by non-magical means while inside the corpse. 

The Yunstreiter may remain inside the corpse until the corpse is destroyed or the Yunstreiter ends it as a bonus action. The Yunstreiter appears in the same space as the corpse if the corpse is destroyed. 

The Yunstreiter can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The Yunstreiter regains spent legendary actions at the start of its turn.

Cursed Slam (1 Action). The Yunstreiter makes one Cursed Claw attack.

Raise Dead (2 Actions). The Yunstreiter targets a humanoid corpse it can see, turning the corpse into a Greater Zombie.

Corpse Bust (3 Actions). The Yunstreiter targets a corpse or undead it can see with 60 feet. The target explodes in a 15 foot radius. Creatures in the radius must succeed a DC 16 Constitution saving throw or take 18 (4d8) acid damage and be poisoned until the end of the Yunstreiter's next turn.