Aincent Mountain Golem

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

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

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

Timeless Existence. Any time-altering spell/effect has no effect on the golem.

Magic Being. The golem's attacks are magical. The golem can cast the following spells (save DC 20, +10 to hit) at will: power word stun, earthquake, dominate monster, control weather, antimagic field, simulacrum, reverse gravity, move earth, flesh to stone, find a path, wall of stone, legend lore, hold monster, hold person, geas, dream, commune with nature, creation, awaken, stone shape, stoneskin, polymorph, locate creature, dominate beast, conjure woodland beings, toungs, speak with plants, slow, remove curse, protection from energy, plant growth, meld into stone, dispell magic, conjure animals, zone of truth, silence, protection from poison, moonbeam, locate object, locate animals or plants, hold person, gust of wind, detect thoughts, calm emotions, blindness/deafness, speak with animals, sleep, sanctuary, protection from evil and good, identify, heroism, goodberry, fog cloud, entangle, create or destroy water, animal freindship.

Multiattack. The golem makes two slam attacks, then casts a spell.

Slam. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 24 (4d6 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 strength saving throw or be knocked prone.

Slow (Recharge 5–6). The golem targets one or more creatures it can see within 160 feet of it. Each target must make a DC 23 Wisdom saving throw against this magic. On a failed save, a target can't use reactions, its speed is halved, and it can't make more than one attack on its turn. In addition, the target can take either an action or a bonus action on its turn, not both. These effects last for 1 minute. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Can take 3 Legendary Actions, choosing from the options below. Only one legendary action can be used at a time, and only at the end of another creature's turn. Spent legendary actions are regained at the start of each turn.

Creation (Costs 3 actions). The golem casts wish spell, but only to create.

Ancient Mage. The golem casts a spell.

Stomp. The golem makes one slam attack if the target is a creature, it becomes incapacitated on a failed save. This effect will end if the golem moves or attacks.