Relentless Assault. The colossus is immune to being banished by any means short of a wish spell.

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

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

Magic Weapons. The colossus' weapon attacks are magical.

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

 Prismatic Reflection. When the colossus is targeted by a spell that deals radiant damage, it reflects half that damage back on other creatures within a 15 ft. radius.

Cognitohazard. Each creature that sees the colossus, must succeed on a DC 17 Wisdom saving throw or become charmed for 1 minute. If the target has the spell casting feature, and fails the save by 5 or more, it falls prone and is incapacitated for an hour. All other creatures run in the opposite direction of the colossus for the duration. If a creature passes the save it is immune to the the colossus' cognitohazard for 24 hours.

Multiattack. The colossus makes two attacks with its columns, one with its tail, and if it is charged, it uses the Luminous Beam

Column. Melee Weapon Attack: +16 to hit, reach 20 ft., 5 ft. square. Hit: 18 (2d10 + 8) bludgeoning damage. Creatures in the space can expend their reaction to attempt to make a Dexterity saving throw against the colossus' attack roll, if the target succeeds it takes half damage.

Tail. Melee Weapon Attack: +16 to hit, reach 20 ft., 1 target. Hit: 20 (3d8 + 8) bludgeoning damage. If a creature is hit by this attack, it must make a contested strength check, or be thrown 15 feet away.

Luminous Beam (Recharge 5-6).The colossus creates a shining bead of gravitational force in its mouth, then releases the energy in a 90-foot line that's 10 ft. wide. Each creature in that area must make a DC 23 Strength saving throw. On a failed save, the creature takes 63 (14d8) radiant damage.

Psionic Expulsion (recharge 5-6). The colossus unleashes an invisible wave, forcing any creature that is not immune to psychic damage to succeed a DC 23 wisdom saving throw or take 30 (4d10 +10) psychic damage. A creature that fails this save by 5 or more is stunned until the end of their next turn.

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

Recharge (Costs 2 Actions). The colossus recharges any spent abilities.

Sweeping attack. The colossus makes a melee attack.

Consume Magic (Costs 2 Actions). The colossus absorbs any spells against it in the last turn, ending the effects and regaining 16 (2d8 + 10) hit points.