Colossal Scorpion

Innate Spellcasting. The scorpion’s innate spellcasting ability is Charisma (spell save DC 20, +12 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: acid splash, arms of hadar, conjure animals (scorpions only), conjure minor elementals (dust mephits only), create or destroy water, dust devil (no concentration, one bonus action to move all), earthbind, enervation, expeditious retreat, hellish rebuke, infestation, nondetection, poison spray, primal savagery, protection from energy (no concentration), ray of enfeeblement (no concentration), ray of sickness, spider climb (no concentration), spike growth, Tasha’s caustic brew

3/day each: conjure minor elementals (no concentration, dust mephits only), dust devil (as a 5th-level spell, no concentration), giant insect, giant insect (no concentration, scorpions only), hold monster, hold person, shadow of moil, vitriolic sphere

1/day each: bones of the earth, hallucinatory terrain, insect plague

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

Magic Reflection. If a spell misses the scorpion, the scorpion can cause the spell to target the creature that cast the spell or a creature within 30 feet of the scorpion. If the scorpion is included in an area of effect that allows it to make a saving throw it has advantage on the saving throw, and if the scorpion would take half damage on a success, it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails. If the colossal scorpion succeeds on a saving throw and takes no damage from the effect the creature that forced the scorpion to make the saving throw, must make the same saving throw against the effect, taking the effects damage as if it had been targeted with the effect on a failed save, or half as much on a successful one.

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

Multiattack. The scorpion makes three attacks: two with its claws and one with its Sting, then it uses its Antilife Shell.

Claw. Melee Weapon Attack: +13 to hit, reach 20 ft., one target. Hit: 17 (2d10 + 6) bludgeoning damage. If the target is a Huge or smaller creature, it is grappled (escape DC 21), until the scorpion uses its Antilife shell. Until this grapple ends the scorpion can't use this claw to make a claw attack against another target, and if the target is Large or smaller it is restrained.

Sting. Melee Weapon Attack: +13 to hit, reach 25 ft., one target. Hit: 16 (3d6 + 6) piercing damage, and the target must make a DC 20 Constitution saving throw. On a failed save, the creature takes 33 (6d10) poison damage and is poisoned until the end of its next turn. On a successful save, the creature takes half as much damage and isn't poisoned. A creature is paralyzed while poisoned in this way.

Antilife Shell. Any creature within 30 feet of the scorpion must make a DC 20 Charisma saving throw (the DC increases to 25 if it is within 20 feet of the scorpion or 30 if the creature is within 10 feet of it) or be pushed to the nearest safe, unoccupied space that is not within 30 feet of the scorpion. Until the start of the scorpion's next turn, if any creature starts its turn while within 30 feet of the scorpion, or moves to a space within 30 feet of the scorpion, it must make a DC 20 Charisma saving throw or be pushed to the nearest safe, unoccupied space that is not within 30 feet of the scorpion. In addition, while this effect is active creatures have disadvantage on attack rolls, Constitution checks and Constitution saving throws while within 30 feet of the scorpion.

While this effect is active the scorpion cannot move within 30 feet of a creature that is not already within 30 feet of it.

This does not affect/apply to constructs, nor creatures conjured by the scorpion. Creatures also automatically fail the saving throws if the scorpion is sleeping.

Frightful Presence. Each creature of the scorpion's choice that is within 120 feet of the scorpion and aware of it must succeed on a DC 20 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, if it is not within 30 feet of the scorpion, 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 scorpion's Frightful Presence for the next 24 hours.

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

Claw. The scorpion makes a claw attack. If the attack hits the creature must repeat its saving throw against the scorpion's Antilife Shell, if it is affected by it.

Frightful Presence. The scorpion uses its Frightful Presence

Move. The scorpion moves up to its speed, however it cannot move within 30 feet of a creature (that isn't a construct, undead or a creature conjured by the scorpion) that is not already within 30 feet of it.

Repel Life. Any creature within 30 feet of the scorpion must make a DC 20 Charisma saving throw (the DC increases to 25 if it is within 20 feet of the scorpion or 30 if the creature is within 10 feet of it) or be pushed to the nearest safe, unoccupied space that is not within 30 feet of the scorpion. This does not affect constructs, undead nor creatures conjured by the scorpion.

At-Will Spell (Costs 2 Actions). The scorpion casts one of its at-will spells.

Sting (Costs 3 Actions). The scorpion makes a sting attack. If the attack hits the creature must repeat its saving throw against the scorpion's Antilife Shell, if it is affected by it.