Castle Colossus

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

Magic Resistance. This colossus has Advantage on Saving Throws against Spells or any other magical Effects.

Magical Weapons. The colossus' weapon attacks are magical.

Multiattack. The colossus can make three slam attacks and one boulder attack. It can make one protect action instead of two slam attack.

Slam. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 25 (3d10 + 8) bludgeoning damage. 

Boulder. Ranged Weapon Attack: +15 to hit, range 90/150 ft., 1 target. Hit: 22 (3d8 + 8) bludgeoning damage.

Protect. The colossus targets an allied creature within 30 ft. of it scoops it and puts it into its castle body.

Safeguard. When allied creatures within 20 ft. of the colossus is targeted by a spell or magical effect that causes them to make a dexterity saving throw, the colossus can intercede upon them and reduce incoming damage by half but receives the damage.

The colossus can take 2 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.

Attack: The colossus makes one slam attack.

Boulder (Costs 2 Actions): The colossus makes one boulder attack.

Protect (Costs 2 Actions): The colossus makes one Protect action.