Marble

Constructed Nature. Marble does not require air, food, drink, or sleep.

Arcane Core. Marble’s body contains an arcane core that provides her with additional spell slots and powers. She has 2 additional 7th-level spell slots that can only be used for spells related to stone, metal, or earth.

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

Immutable Form. Marble is immune to any spell or effect that would alter her form.

Spellcasting. Marble is a 16th-level spellcaster. Her spellcasting ability is Intelligence (spell save DC 19, +11 to hit with spell attacks). Marble has the following Wizard spells prepared:
Cantrips (at will): Fire Bolt, Ray of Frost, Mage Hand, Minor Illusion, Mending  
1st level (4 slots): Shield, Magic Missile, Absorb Elements, Detect Magic
2nd level (3 slots): Misty Step, Mirror Image, Shatter, Scorching Ray
3rd level (3 slots): Counterspell, Dispel Magic, Fireball, Lightning Bolt
4th level (3 slots): Stone Shape, Greater Invisibility, Wall of Fire
5th level (3 slots): Cone of Cold, Animate Objects, Wall of Force
6th level (2 slots): Chain Lightning, Disintegrate
7th level (2 slots +2 from Arcane Core): Teleport, Finger of Death, Delayed Blast Fireball, Reverse Gravity, Earthquake
8th level (1 slot): Maze, Sunburst
9th level (1 slot): Meteor Swarm, Time Stop

Multiattack. Marble makes three attacks with her Stonefist or two with her Earthshatter Maul.

Stonefist. Melee Weapon Attack: +11 to hit, reach 10 ft., 1 target. Hit: 18 (3d8 + 5) bludgeoning damage. 

Earthshatter Maul: Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 27 (5d8 + 5) bludgeoning damage. On a hit, the target must succeed on a DC 20 Constitution saving throw or be stunned until the end of Marble’s next turn.

Stone Shard Storm (Recharge 5-6): Marble slams her fists into the ground, causing jagged stone shards to erupt in a 30-foot radius centered on her. Each creature in the area must make a DC 20 Dexterity saving throw, taking 45 (10d8) piercing damage on a failed save, or half as much damage on a successful one.

Gravitic Pulse (1/Day): Marble emits a pulse of gravitational force in a 60-foot radius. Each creature within the radius must make a DC 20 Strength saving throw. On a failed save, the creature is pulled 30 feet closer to Marble and is restrained for 1 minute. A restrained creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Arcane Reservoir. Marble can store spell energy within her body, allowing her to regain expended spell slots as a bonus action. She can regain a total of 3 levels of spell slots once per day (for example, a 3rd-level spell slot or three 1st-level spell slots).

Arcane Shielding: When Marble is targeted by a spell or attack that would deal radiant or necrotic damage, she can use her reaction to reduce the damage by 2d10 + 7.

Marble 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. Marble regains spent legendary actions at the start of her turn.

Cantrip: Marble casts a cantrip.

Stone's Resilience: Marble ends one condition on herself (except for petrified) or regains 30 hit points.

Stone Slam (Costs 2 Actions): Marble slams her stone fists into the ground, causing tremors. Each creature within 20 feet must make a DC 18 Dexterity saving throw or take 2d10 bludgeoning damage and be knocked prone.