Apparition

Incorporeal Movement. The apparition 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.

Ethereal Tether. On initiative turn 20 (losing to ties), the apparition returns to the ethereal plane. While on the ethereal plane the apparition can neither attack nor be attacked by creatures on the prime material plane. 

Deathly Fright. The apparition makes a psychic attack against a creature it can see within 60'. The target must make a DC 16 Wisdom saving throw or take 21 (4d8 + 3) psychic damage. and the target is [Tooltip Not Found] until the end of the apparition's next round. . If the target is stunned when attacked, the target is reduced to 0 Hit Points. If the target succeeds in its saving throw then it takes half damage instead and is no longer stunned if it was stunned. The apparition can only make this attack against a creature on rhe same plane as it.

Create Apparition. Any creature who is killed by an apparition and has not been revived or resurrected within an hour will enter the ethereal plane as an apparition, their body fading to nothing, leaving any equipment carried behind. 

Ethereal Ambush. As a bonus action, the apparition can travel from the ethereal plane to the prime material plain or vice versa. The apparition is nearly invisible until using its Deathly Fright power and has advantage from surprise on its attack if moving to the plane and making the attack on the same turn.