Clockwork_centipede

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

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

Damage resistances All but force, radiant and psychic.

Damage Immunities Acid, Fire, Necrotic, Poison; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks.

Condition Immunities Charmed, Exhaustion, Paralyzed, Incapacitated, Frightened, Petrified, Poisoned, Stunned.

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

Senses Truesight 120 ft., Passive Perception 12

Siege Monster. The centipede  deals double damage to objects and structures.

Writhing Terror. Any enemy that starts its turn within 30 feet of the centipede must succeed on a DC 26 Wisdom saving throw or be frightened until the start of the enemy’s next turn. If the enemy’s saving throw is successful, it is immune to this centipede ’s Writhing Terror for the next 24 hours.

Multiattack. The centipede  makes five attacks — one with its slam, one with a tail swing, and two with its Gear Blasts — and then uses Stomp.

Slam. Melee Weapon Attack: +18 to hit, reach 20 ft., one target. Hit: 29 (3d12 + 10) bludgeoning damage, and the centipede  can push the target up to 20 feet away from it.

Tail Swing. Ranged Weapon Attack: +18 to hit, reach 60 ft., one target. Hit: 29 (3d12 + 10) bludgeoning damage, and the centipede can push the target up to 20 feet away from it. With a swift movement of its tail, the centipede hurls a blast of bolts that fly towards its enemies, followed by a wave of air that can push creatures away. There is a 1 in 4 chance that the bolts will explode on impact, causing an extra 3d6 of damage.

Gear blast Ranged Spell Attack: +18 to hit, range 300 ft., one target. Hit: 18 (4d8) force damage, and if the target is a creature, it is knocked prone.

Stomp. The centipede stomps one of its feet at a point on the ground within 20 feet of it. Any creature in a 60-foot-radius, 60-foot-high cylinder centered on this point must succeed on a DC 26 Dexterity saving throw or take 33 (6d10) bludgeoning damage and fall prone. Until the centipede uses its Stomp again or moves, the creature is restrained. While restrained in this way, the creature (or another creature within 5 feet of it) can use its action to make a DC 26 Strength check. On a success, the creature relocates to an unoccupied space of its choice within 5 feet of the centipede and is no longer restrained.

Structures, as well as nonmagical objects that are neither being worn nor carried, take the same amount of damage if they are in the cylinder (no save).

Incinerating Beam (Recharge 5–6). The centipede fires a beam of energy in a 150-foot line that is 10 feet wide. Each creature in the line must make a DC 26 Dexterity saving throw, taking 60 (11d10) radiant damage on a failed save, or half as much damage on a successful one. A creature reduced to 0 hit points by this beam is disintegrated, leaving behind anything it was wearing or carrying.

Deflect As a reaction against spell attacks that require a ranged attack roll, the centipede can turn one of its carapace sections towards the origin of the spell and deflect it, suffering no damage.

There is a 2 in 6 chance of the spell being deflected back to the caster and causing the damage intended for the centipede.

Leg swarm: Once per round, at any point during combat, the centipede can detach one of its legs and throw it as an  explosive bomb effect. Range 60ft. AOE 20ft. Characters within the AOE must succeed a DEX save DC 20 or take 6d6 piercing damage from the flying metal. Half the damage on a successful save.

Screw cluster: Once each 6 rounds the centipede throws a cluster of metallic shards that deal 10d6 damage to characters within the AOE (20ft)  who fail a save. Range: 60ft

Each creature in the AOE must make a DC 19 Dexterity saving throw, taking 15 (5d6) bludgeoning damage on a failed save, or half as much damage on a successful one.