Caulda, the Scourge

Legendary Resistance (3/Day). If Caulda fails a saving throw, it can choose to add a d12 to that roll, potentially turning a failure into a success.

Magic Resistance. Caulda has advantage on saving throws against spells and other magical effects.

Immutable Form. Caulda is immune to any spell or effect that would alter its form.

Death Burst. When Caulda dies, it explodes in a burst of fire and magma. Each creature within 20 feet of it must make a DC 22 Dexterity saving throw, taking 35 (10d6) fire damage on a failed save, or half as much damage on a successful one. Flammable objects that aren't being worn or carried in that area are ignited.

Heated Body. A creature that touches Caulda or hits it with a melee attack while within 5 feet of it takes 11 (2d10) fire damage.

Illumination. As a bonus action, Caulda can set itself ablaze or extinguish its flames. While ablaze, Caulda sheds bright light in a 20-foot radius and dim light for an additional 20 feet.

Multiattack. Caulda can use its Frightful Presence. It then makes three attacks with its Blazing Fist.

Blazing Fist. Melee Weapon Attack :+17 to hit, reach 5ft., one target. Hit: 20 (2d10 + 9) bludgeoning damage, plus 36 (8d8) fire damage.

Inferno Breath (Recharge 5–6).  Caulda exhales blue fire in a 60-foot cone. Each creature in that area must make a DC 22 Dexterity saving throw, taking 70 (20d6) fire damage on a failed save, or half as much damage on a successful one.

Frightful Presence.  Each creature, of Caulda’s choice, within 120 feet of it and aware of it must succeed on a DC 23 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if Caulda is within line of sight, 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 Caulda's Frightful Presence for the next 24 hours.

Summon Ally (1/day). Caulda lets out a roar that echoes out into the planes. As it does so, it summons either: 2d4 Magmin, 1d6 Hell Hounds or 1d4 fire elementals. The chosen creatures appear in a burst of harmless flame no more than 10 feet from Caulda. All creatures summoned in this way by Caulda obey its commands, and act as an ally of Caulda. They remain for 1 minute, or until Caulda dismisses them as an action.

Constant Engine. Caulda can take a bonus action to take the Dash or Disengage action.

Caulda 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. Caulda regains spent legendary actions at the start of its turn.

Detect. Caulda makes a Wisdom (Perception) check.

Move. Caulda can move up to half its speed.

Shifting Inferno (Costs 2 actions). Caulda stamps its foot down, sending ripples through the earth. Each creature within 15 feet of Caulda must succeed on a DC 22 Dexterity saving throw or take 18 (2d8 + 9)  bludgeoning damage and be knocked prone. Caulda can then move up to half its movement speed.