Arena Master

One with the Arena. Once per turn without taking an action the Arena Master can transform and shape the arena at will. This can be making a hole, extruding an area, etc. However whatever he chooses to do to the arena must respect the size condition of 27 ft

Master's Awareness. The Arena Master knows the exact position of all creatures on the battlefield, even if hidden or invisible, as long as they are within 120 ft. In addition he doesn't suffer disadvantage when attacking invisible or unseen targets within this area.

Multiattack. The Arena Master makes three attacks, using Arcane Burst or Gauntlet Smash in any combination.

Arcane Burst. Melee or Ranged Attack Roll: +12, reach 5 ft. or range 120 ft. Hit: 18 (2d12 + 5) Force damage.

Gauntlet Smash. Melee Attack Roll: +12, reach 5 ft. Hit: 15 (3d6 + 5) Force damage.

Spellcasting. The Arena Master casts one of the following spells, using Intelligence as the spellcasting ability (spell save DC 20):

At Will: Thunderwave, Darkness, Erupting Earth, Fireball (level 5 version), Invisibility, Lightning Bolt (level 5 version), Mage Hand, Prestidigitation

Protective Magic. The Arena Master casts Counterspell or Shield in response to the spell’s trigger, using the same spellcasting ability as Spellcasting.

These legendary actions use a times per day system.

3/Day Teleport. The Arena Master teleports up to 60 feet to an unoccupied space it can see, and each creature within 10 feet of the space it left takes 11 (2d10) Force damage, and the target is pushed 15 ft away.

2/Day Terrain Jolt. Dexterity Saving Throw: DC 20, each creature in a 20-foot Emanation originating from a certain point up to 60 ft away from the Arena Master. Failure: 31 (9d6) Force damage. Success: Half damage.

5/Day Raise the Stakes. The Arena Master transforms a 30 ft area within 60 ft of him into a trap (spike pit, lava geyser, unstable platforms, etc.) . This trap deals 14 (4d6) the damage type depends on the trap.