Ghost Shark

Blood Frenzy. The ghost has advantage on melee attack rolls against any creature that doesn't have all its hit points. 

Ethereal Sight. The ghost can see 120 feet into the Ethereal Plane when it is on the Material Plane, and vice versa.

Incorporeal Movement. The ghost can move through other creatures and objects as if they were difficult terrain. It takes 16 (3d10) force damage if it ends its turn inside an object.

Withering Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 16 (2d10 + 5) piercing damage plus 5 (1d10) necrotic damage.

Etherealness. The ghost enters the Ethereal Plane from the Material Plane, or vice versa. It is visible on the Material Plane while it is in the Border Ethereal, and vice versa, yet it can't affect or be affected by anything on the other plane.

Horrifying Visage. Each non-undead creature within 60 feet of the ghost that can see it must succeed on a DC 14 Wisdom saving throw or be frightened for 1 minute. If the save fails by 5 or more, the target also ages 1d4 × 10 years. A frightened target can repeat the saving throw at the end of each of its turns, ending the frightened condition on itself on a success. If a target's saving throw is successful or the effect ends for it, the target is immune to this ghost's Horrifying Visage for the next 24 hours. The aging effect can be reversed with a greater restoration spell, but only within 24 hours of it occurring.

Frenzy (Recharge 6). One creature that the ghost can see within 30 feet of it must succeed on a DC 14 Charisma saving throw.  A creature automatically succeeds if it is immune to being frightened or charmed.  On a failed save, the target is stirred into a frenzied state and loses the ability to distinguish friend from foe, regarding all creatures it can see as enemies until the effect ends. Each time the target takes damage, it can repeat the saving throw, ending the effect on itself on a success.

Whenever the affected creature chooses another creature as a target, it must choose the closest creature it can see within range of the attack, spell, or other ability it’s using.  If the closest creature is out of range, the affected creature pursues the nearest creature to the best of its ability.  If an enemy provokes an opportunity attack from the affected creature, the creature must make that attack if it is able to.

The frenzy lasts until the creature drops to 0 hit points, the ghost ends it as a bonus action, or the ghost's influence is turned or forced out by an effect like the dispel evil and good spell.  The target is immune to this ghost's Frenzy for 24 hours after succeeding on the saving throw or after the frenzy ends.