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

Regeneration. When he is at zero hit points, Vildbjorn regains 10 hit points at the start of its turn as torgrind-infused rocks agglomerate to him. Vildbjorn dies only if it starts its turn with 0 hit points and Trickfoot's torgrind-barbed spear has been removed from his heart. The spear is removable only with a DC 20 Athletics check.

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

Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 28 (4d8 + 8) piercing damage. If the target is Large or smaller, it must succeed on a DC 19 Strength saving throw or be restrained. Only one creature may be so restrained at a time, and while the creature is restrained Vildbjorn may not make bite attacks against any other creature.

Claw. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 24 (4d6 + 8) slashing damage. If the target is Large or smaller, it must succeed on a DC 19 Dexterity saving throw or be knocked prone.

Sundering Quake (Recharge 5-6). Vildbjorn slams his claws into the earth, causing jagged spikes of torgrind to erupt in a 60-foot line that is 20 feet wide. Each creature in that area must make a DC 21 Dexterity saving throw, taking 33 (6d10) bludgeoning and 33 (6d10) necrotic damage on a failed save, or half as much damage on a successful one.

Vildbjorn 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. Each legendary action can only be used once per round. Each legendary action uses a summoned torgrind spike; if there are no more torgrind spikes, Vildbjorn cannot use legendary actions until more have been summoned. Vildbjorn regains spent legendary actions at the start of its turn.

Psychic Spike. The targeted creature must make a DC 17 Intelligence saving throw, taking 36 (8d8) psychic damage on a failed save.

Planar Mists. Fog rolls into a 20-foot radius circle of Vildbjorn's choosing, and inside is a creature of CR2, or two CR1, that has been ripped from somewhere on the material plane. It is likely to be hostile.

Blinding Flash. All creatures within 120 feet of the spike that can see it must make a DC 17 Constitution save. On a failed save, they are blinded until the end of Vildbjorn's next turn.