Colossal Bear

Aura of Vengeance. If a fiend or undead starts its turn within 30 feet of the bear, it must make a DC 27 Charisma saving throw. On a failed save, the creature can't use its bonus action, nor legendary actions (if it has them), it can only use its action to take the Attack (one weapon attack only), Dash, Disengage, Dodge, Hide, or Use an Object action, and its speed is halved until the start of its next turn.

If a fiend or undead ends its turn while within 30 feet of the bear, it must make a DC 27 Charisma saving throw, or it must remain within 30 feet of the bear (a fiend that id conjured within 30 feet of the bear has disadvantage on the saving throw). If the bear moves so that an affected creature is no longer within 30 feet of the bear, the creature is pulled towards the bear so that it remains within 30 feet of the bear.

If a fiend or undead forces a creature, within 30 feet of the bear, to make a saving throw, the bear can grant the creature advantage on the saving throw (no action required). Any damage dealt to fiends and undead, within 30 feet of the bear, ignores resistances and immunities. Fiends and undead have disadvantage on attack rolls, ability checks, and saving throws, have vulnerability to radiant damage, and can't become invisible, while within 30 feet of the bear. When a fiend or undead hits a creature, within 30 feet of the bear, with an attack or forces it to make a saving throw, it takes 9 (2d8) radiant damage. If a fiend or undead is not in its true form, while within 30 feet of the bear, it instantly reverts to its true form and can’t assume a different form until it is more the 30 feet away from the bear and the bear is not within its line of sight. If a fiend or undead attempts to teleport, while within 30 feet of the bear, it is instead banished to Carceri. Corpses, and other remains can't be turned into undead while within 30 feet of the bear, and if a creature dies while within 30 feet of the bear it can't become undead.

Celestial Aura. Divine energy radiates from the bear. Each creature of the bear's choice, has advantage on death saving throws, Strength checks and Strength saving throws, resistance to necrotic damage, immunity to poison damage, immunity to the blinded, charmed, deafened, frightened, paralyzed poisoned, and stunned conditions, can't become diseased or possessed, can't have its hit point maximum reduced, and deals an extra (1d4) radiant damage when it hits with a weapon attack, while within 30 feet of the bear. In addition, each creature of the bear's choice, while within 30 feet of the bear, regains 7 (2d6) hit points or gains 10 temporary hit points, at the start of each of its turns.

Innate Spellcasting. The bear’s innate spellcasting ability is Wisdom (spell save DC 27, +19 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: absorb elements (as a 3rd-level spell), animal friendship (as a 3rd-level spell), animal messenger (as a 9th-level spell), barkskin, beast sense, create food and water, earth tremor (as a 5th-level spell), enhance ability (bear’s endurance only, no concentration), guiding bolt, light, protection from poison, purify food and drink, resistance, sacred flame

3/day each: charm monster, conjure animals (as a 5th-level spell), daylight, healing spirit (as a 3rd-level spell), moonbeam, primordial ward (no concentration), summon beast (as a 5th-level spell)

1/day each: absorb elements (as a 5th-level spell), animal shapes (no concentration), awaken, bones of the earth, conjure fey, dawn, destructive wave, investiture of stone, stoneskin (no concentration), sunbeam, sunburst, wrath of nature (no concentration)

Keen Smell. The bear has advantage on Wisdom (Perception) checks that rely on smell.

Legendary Resistance (4/Day). If the bear fails a saving throw, it can choose to succeed instead.

Speak with Beasts. The bear can communicate with beasts as if they shared a language.

Telepathic Bond. If the bear communicates with a creature telepathically, the creature can respond to the bear, and other creatures in the conversation, likewise.

Titan's Stability. The bear can only become prone if it wishes to be.

Will of the Ancient One. If a creature spends at least 1 minute (10 turns) within 30 feet of the bear, and gains the benefit from the bear's Celestial Aura, it gains the mark of the bear. The mark of the bear lasts on a creature for a number of days equal to the number of hours (rounded up) the creature spent within 30 feet of the bear. If a creature, with the mark of the bear, targets a good creature with an attack or a harmful spell or includes it in the area of effect of a harmful spell, it must first make a DC 27 Wisdom saving throw. On a failed save, the creature must choose a new target or take a different action. A creature with the mark of the bear can't cast spells or use features that would create undead or conjure fiends.

In addition, a creature with the mark of the bear has advantage on Wisdom (Animal Handling) checks, Charisma (Persuasion) checks — made to persuade a good creature, and Intelligence checks — made to recall information about undead. If an evil creature forces a creature with the mark of the bear, to make a saving throw, it makes the saving throw with advantage.

Multiattack. The bear makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 32 (4d10 + 10) piercing damage.

Claw. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 28 (4d8 + 10) slashing damage plus 7 (2d6) radiant damage. If the target is a creature, the bear can choose one of the following additional effects:

• The target becomes visible if it is invisible, and can't become invisible for 1 minute.
• The target must succeed on a DC 27 Constitution saving throw or be blinded for 1 minute. The creature can repeat the saving throw at the end of each of its turns, ending the effect on a success.
• The target must succeed on a DC 27 Wisdom saving throw or be frightened for 1 minute. The creature can repeat the saving throw at the end of each of its turns, ending the effect on a success.
• The target must succeed on a DC 27 Constitution saving throw or be stunned until the end of the creature's next turn.
• The target must make a DC 27 Strength Saving throw. On a failed save, the creature is pushed 30 feet away from the bear and is knocked prone. On a successful save, the target is pushed 15 feet away from the bear and isn't knocked prone.
• The target, if it has 50 hit points or less, it must make a DC 27 Charisma saving throw. On a failed save, if the target is not on its native plane of existence, the target disappears, returning to its native plane; if the target is an undead, the target is banished to the Shadowfell; if the target is on its native plane and its not an undead, it vanishes into a harmless demiplane, it remains there for 1 minute, at which point the target reappears in the space it left or in the nearest unoccupied space if that space is occupied.

Noble Roar. Each evil creature of the bear's choice that is within 120 feet of the bear and aware of it must succeed on a DC 27 Wisdom saving throw or become frightened and turned for 1 minute (a creature that is deafened automatically succeeds on the saving throw if the bear is not within line of sight).

A turned creature must spend its turns trying to move as far away from the bear as it can, and it can’t willingly move to a space within 30 feet of the bear. It also can’t take reactions. For its action, it can use only the dash action or try to escape from an effect that prevents it from moving. If there’s nowhere to move, the creature can use the dodge action.

A creature can repeat the saving throw at the end of each of its turns, if the bear is not within line of sight and is more than 120 feet away from it, ending the effect on itself on a success (the creature has advantage on the saving throw if it is deafened). If a creature's saving throw is successful or the effect ends for it, the creature has advantage on the saving throw against the bear's Noble Roar for the next hour.

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

At-Will Spell. The bear casts one of its at-will spells.

Attack. The bear makes a bite or claw attack.

Move. The bear moves up to its speed.

Noble Roar. The bear uses its Noble Roar.

Charge (Costs 2 Actions). The bear moves up to its speed and makes a claw attack.

Spell (Costs 3 Actions). The bear casts one of its spells.

Bear's Endurance (Costs 3 Actions). The bear gains 30 temporary hit points, and each creature of the bear's choice, within 30 feet of the bear, gains 15 temporary hit points. A creature has advantage on Constitution saving throws while it has these hit points.