Crimson Mist Hound

Pack Tactics. The hound has Advantage on an attack roll against a creature if at least one of the hound’s allies is within 5 feet of the creature and the ally doesn’t have the Incapacitated condition.

Red Mist Shroud. While the hound has more than half its hit points remaining, it continuously secretes a thin mist from its skin, creating a 30-foot radius of lightly obscuring red mist around it. This mist moves with the hound and dissipates if its hit points drop to half or below. While within this mist, it is almost impossible to discern the direction of any sounds made within it. All sound echoes around its hapless victims.

Blood Boon. While Red Mist Shroud  is active, the Crimson Mist Hound and any Mist Hounds within its mist gain a +1 bonus to attack and damage rolls. This bonus increases by 1 each time the mist hound uses Cannibalize, up to a maximum of +5.

Fog Mind. The hound can navigate through Mist Shroud as if it was clear, using the fog itself to "feel" the environment it envelops. Due to its seamless connection to its red mist, it is impossible to hide within its mist. As it is the hounds themselves that disperse sound throughout the fog, the hounds can hear normally as well.

Mending Mist. While Mist Shroud as active, the hound regains 8 hit points at the start of each of its turns.

Shrouding Convergence. When two or more Mist Hounds are within 10 feet of each other, their mist shrouds merge, thickening into heavy fog. The radius of their combined Mist Shroud  increases by 5 feet for each additional mist hound beyond the first, and the area within it becomes heavily obscured instead of lightly obscured.

Bite. Melee Attack Roll: +8, reach 5 ft. Hit: 8 (2d8 + 5) Piercing damage. Hit: 5 (2d4) Necrotic damage. If the target is a Large or smaller creature, it has the Prone condition.

Cannibalize. As an action, the Crimson Mist Hound devours a mist hound within 5 feet of itself, gaining 3d10 temporary hit points. Each creature within the mist must make a DC 18 Wisdom saving throw or become frightened for 1 minute as the gruesome sounds of the Crimson Mist Hound viciously gorging on the flesh of its kin loudly echoes through the fog. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on a success. Additionally, this act empowers Blood Boon.

Drag. Immediately after hitting a creature with a bite attack, the hound can use a bonus action to drag the target up to 10 feet in any direction, provided the target was already prone.

Echoing Howl. A mist hound can mimic the voice of any creature it has heard within the past 24 hours. A creature that hears this can make a Wisdom (Insight) check against a DC 18 to recognize the sound as an imitation. A creature within a pack's Shrouded Convergence has disadvantage on this check.

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

Phantom Pack (2 Actions/Once Per Long Rest)
The Crimson Mist Hound conjures three ephemeral copies of itself from the surrounding mist. Each copy has 1 hit point, shares the hound's AC, and disappears if it takes any damage. The copies act on the crimson mist hound's turn and can make melee attacks with a +6 bonus to hit, dealing 1d8 + 4 piercing damage on a hit. The copies fade after 1 minute or until destroyed.

Misty Haze (1 Action)
The Crimson Mist Hound can teleport up to 30 feet to an unoccupied space within its Red Mist Shroud or Shrouding Convergence.