Argenus

Precognitive Mind. Argenus can cast any Divination spell at will, this does not cost spell slots.

Seeker of Knowledge. Argenus is proficient with the Altar of the Astute Diviner.

Spellcasting. Argenus is a 20th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 21, +13 to hit with spell attacks).

Cantrips (at will): Mage Hand, Prestidigitation, Dancing Lights, Light, Minor Illusion
1st level (4 slots): Find Fimiliar, Floating Disk, Unseen Servant, Magic Missile
2nd level (3 slots): Arcane Lock, Continual Flame, Spider Climb
3rd level (3 slots): Glyph of Warding, Counterspell, Dispel Magic
4th level (3 slots): Control Water, Fabricate, Resilient Sphere
5th level (3 slots): Teleportation Circle, Creation, Telekenisis
6th level (2 slots): Disintegrate, Globe of Invulnerability
7th level (2 slots): Plane Shift, Forecage
8th level (1 slot): Control Weather
9th level (1 slot): Wish

Rough Skin. Non-magical weapons that aren't made out of adamantite that hit Argenus will gain a stack of dullness. At 5 stacks, the weapon is no longer able to deal damage but it isn't broken.

Legendary Resistance (5/day). Whenever Argenus fails a saving throw, it can choose to succeed instead.

Magic Weapon. Argenus's attacks are considered magical.

Pinch. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 21 (6d6 + 5) bludgeoning damage and the target is grappled. At the start of the targets turn it can succeed on a DC 18 Strength/Acrobatics check to escape from the grapple.

Fling. RangedWeapon Attack: a creature grappled by pinch is flung away up to 60 feet. Any creature in its path must succeed on a DC 16 Dexterity saving throw or be hit by the creature, taking 1d6 bludgeoning damage for every 10 feet the creature was flung. The creature that was flung takes also takes this damage if it hits a creature or hits an object.

Caridoid Escape. When targeted with an attack, Argenus moves back up to 60 feet without provoking opportunity attacks. If submerged the distance increases to 120 feet.

Argenus has 3 Legendary Actions that it can use at the end of another creature's turn. It regains used Legendary Actions at the start of its turn.

Pinch (1 Action). Argenus uses Pinch.
Fling (1 Action). Argenus uses Fling.
Move (1 Action). Argenus moves up to its speed.
Cast Spell (2 Actions). Argenus casts spell of 8th level or lower.
Divinate (3 Actions). Argenus looks into every possible future, gaining advantage on all rolls until the end of its next turn.