Wendigo

Shapechanger. If the wendigo is in its realm, it can use its action to polymorph into a Medium cloud of mist, or back into its true form.

While in mist form, the wendigo can't take any actions, speak, or manipulate objects. It is weightless, has a flying speed of 60 feet, can hover, and can enter a hostile creature's space and stop there. In addition, if air can pass through a space, the mist can do so without squeezing, and it can't pass through water. It has advantage on Strength, Dexterity, and Constitution saving throws, and it is immune to all nonmagical damage.

Legendary Resistance (3/Day). If the wendigo fails a saving throw, it can choose to succeed instead.

Misty Escape. When it drops to 0 hit points outside its bone shrine, the wendigo transforms into a cloud of mist (as in the Shapechanger trait) instead of falling unconscious, provided that it is in its realm. If it can't transform, it is destroyed.

While it has 0 hit points in mist form, it can't revert to its wendigo form, and it must reach its bone shrine within 2 hours or be destroyed. Once in its bone shrine, it slowly reforms into its wendigo form. It is paralyzed until it regains at least 1 hit point. After spending 1 hour in its bone shrine with 0 hit points, it regains 1 hit point.

Regeneration. The wendigo regains 20 hit points at the start of its turn if it has at least 1 hit point and is in its realm. If the wendigo takes fire or radiant damage or damage from holy water, this trait doesn't function at the start of the wendigo's next turn.

Spider Climb. The wendigo can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Turning Defiance. The wendigo and any ghouls within 30 feet of it have advantage on saving throws against effects that turn undead.

Wendigo Weaknesses. The wendigo has the following flaws:

Bounded Soul. The wendigo takes 20 radiant damage if it ends its turn outside of its realm.

Ensouled Shrine. If the wendigo's bone shrine is ever destroyed, the wendigo immediately dies as its soul is released, and its realm slowly returns to normal over the course of 1 week.

Blighted Realm. The wendigo has a realm roughly 5 miles wide, which drives the following abilities:

Tainted Ground. Food and drink do not satisfy hunger or thirst in the wendigo's realm, and do not provide nourishment. Creatures that need to eat or drink suffer exhaustion as though they have not had any food or water while in the wendigo's realm.

Still Air. Creatures in the wendigo's realm must succeed on a DC 10 Constitution saving throw at the end of each hour or gain one level of exhaustion. Creatures with resistance or immunity to cold damage automatically succeed on the saving throw, as do creatures wearing cold weather gear (thick coats, gloves, and the like) and creatures naturally adapted to cold climates.

Aura of Death. Creatures other than the wendigo only receive half of the regular healing (minimum 1). If something attempts to resurrect a creature in the wendigo's realm, it must succeed on a flat DC 10 check, otherwise the creature is not resurrected.

Multiattack. (Wendigo Form Only). The wendigo makes two attacks, only one of which can be a bite attack.

Claw (Wendigo Form Only). Melee Weapon Attack: +9 to hit, reach 10 ft., one creature. Hit: 8 (1d8 + 4) slashing damage plus 3 (1d6) cold damage. Instead of dealing damage, the wendigo can grapple the target (escape DC 18).

Bite (Wendigo Form Only). Melee Weapon Attack: +9 to hit, reach 5 ft., one creature. Hit: 7 (1d6 + 4) piercing damage plus 10 (3d6) necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the wendigo regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Frightful Presence. Each creature of the wendigo's choice that is within 60 feet of the wendigo and aware of it must succeed on a DC 17 Wisdom saving throw or become Frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the wendigo's Frightful Presence for the next 24 hours.

Hungering Dead (1/Day). The wendigo magically calls 1d4+1 ghouls (ghoul), provided that the wendigo is in its realm. The called creatures arrive in 1d4 rounds, acting as allies of the wendigo and attacking all other creatures. They remain for 1 hour, until the wendigo dies, or until the wendigo dismisses them as a bonus action.

The wendigo 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 wendigo regains spent legendary actions at the start of its turn.

Wind Walk. The wendigo shifts into its mist form and moves up to its speed without provoking opportunity attacks. It changes back into its wendigo form upon arrival.

Claw. The wendigo makes one claw attack.

Bite (Costs 2 Actions). The wendigo makes one bite attack.