Valus

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

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

Legendary Resistance (1/Day). If Valus fails a saving throw, it can choose to succeed instead.

Siege Monster. Valus deals double damage to objects and structures.

Multiattack. Valus makes two attacks, one with its slam and one with its stomp.

Slam. Melee Weapon Attack:  +8 to hit, reach 20 ft., one target. Hit: 24 (3d12+5) bludgeoning damage and the colossus can push the target up to 20 feet away from it. 

Stomp. The colossus stomps one of its feet at a point on the ground within 20 feet of it. Any creature in a  15-foot-radius, 20-foot-high cylinder centered on this point must succeed on a DC 16 Dexterity saving throw or take 33 (6d10) bludgeoning damage and fall prone. 

Crumbling Colossus. When the colossus drops to 0 hit points, it crumbles and is destroyed. Any creature on the ground within 30 feet of the crumbling colossus must make a DC 19 Dexterity saving throw, taking 22 (4d10) bludgeoning damage on a failed save, or half as much damage on a successful one.

Valus can take 2 legendary actions, choosing from the options below. Only one legendary option can be used at a time and only at the end of another creature's turn. Valus regains spent legendary actions at the start of its turn.

Move. Valus moves up half its speed without provoking opportunity attacks.

Shake. Every creature in the colossus space must make a DC 16 Strenght saving throw. On a failure, the target is knocked prove (It has to use Move first).

Stomp. The colossus stomps one of its feet at a point on the ground within 20 feet of it. Any creature in a  20-foot-radius, 20-foot-high cylinder centered on this point must succeed on a DC 16 Dexterity saving throw or take 33 (6d10) bludgeoning damage and fall prone.