Conquitius

Creator of the elements: Can summon four elementals of his choice. Can only use this feat once per day.

Master of the Elements: Can choose whether it's slam attack deals bludgeoning, cold, fire, lighting, piercing, slashing, or thunder damage.

Elemental Form: Can squeeze through any space one inch wide. In addition, any creature within five feet of it can either be caught on fire for 1d10 damage until doused, be thrown 10 ft from it and take 1d6 bludgeoning damage, be knocked prone, or grappled and take 2d8 +4 damage unless it succeeds on a DC 18 Strength saving throw.

Siege Monster: Deals double damage to buildings and objects

Illumination: Shines 30 ft of bright light around it

 Spellcasting. The [monster name] is a 20-level spellcaster. Its spellcasting ability is Charisma, DC 21, +12 to attack. Conquituis has following spells prepared:
Cantrips (at will): [Acid Splash], [Fire  Bolt], [Frostbite], [Gust], [Mold Earth]                         

1st level (4 slots): [Chaos Bolt], [Earth Tremor], [Faerie Fire], [Ice Knife]                             

2nd level (3 slots): [Flame Blade], [Flame Sphere], [Scorching Ray]                                       

3rd level (3 slots): [Call Lightning], [Fireball], [Tidal Wave]                                                     

4th level (3 slots): [Conjure Minor Elementals], [Elemental Bane], [Wall of Fire]                 

5th level (3 slots): [Cloudkill], [Cone of Cold], [Maelstrom]                                                     

6th level (2 slots): [Sunbeam], [Otiluke's Freezing Sphere]                                                     

7th level (2 slots): [Firestorm], [Whirlwind]                                                                                 

8th level (1 slot): [Tsunami]                                                                                                           

9th level (1 slot): [Meteor Swarm]

Multiattack: Makes three slam attacks

Slam Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 44 (6d8 + 8) damage. 

Flurry of Elements (Recharges 6 turns)  Conquitis shoots off four beam of elements one of each, into four different directions 80ft long, 10ft wide. Each creature in the area must make a DC 22 Dexterity saving throw taking 90(20d8 +8) fire,cold, bludgeoning, or piercing damage on a failed save, or half as much on a successful save.

Shockwave: Conquitis jumps 80 ft in the air. Each creature within an 80ft radius must make a DC 20 Dexterity saving throw or be either knocked prone or caught on fire and take 64(10d10 +8) bludgeoning damage

Conquitis 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. Conquitis regains spent legendary actions at the start of their turn.

Legendary Resistance (3/day). If Conquitis fails a saving throw, he can choose to succeed instead.

Shockwave Attack (Costs 1 Actions). Conquitis makes a Shockwave attack

Overwhelm (Costs 1 Actions). Coquitis chooses either one of the following actions:

Trap: To grapple a creature in place for 1d4 turns unless they make a DC 21 Strength saving throw.

Hurl: Throw a creature into the air to 60ft unless they make a DC 21 Dexterity saving throw.

Engulf: Surround a creature in flames catching them on fire and making them take (2d10 +4) fire damage and (1d10) fire damage every turn they're on fire unless they make a DC 21 Dexterity saving throw.

Suffocate: Drown  a creature in water having the creature take (2d6+6) bludgeoning damage for three turns unless they make a DC 21 Constitution saving throw.

Primal Forces (Costs 3 Actions). Regenerate 60 HP