Corrupter of Worlds

Spellcasting. The Corrupter of Worlds is a 10th-level spellcaster. Its spellcasting ability is wisdom (spell save DC 21, +13 to hit with spell attacks). The Corrupter of Worlds has following druid spells prepared: 

Cantrips (at will): Druidcraft, Mold Earth, Poison Spray
1st level (4 slots): Absorb Elements, Entangle
2nd level (3 slots): Hold Person, Moonbeam
3rd level (3 slots): Erupting Earth, Haste*
4th level (3 slots): Blight
5th level (2 slots): Contagion

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

Legendary Resistance (3/Day). If the Corrupter fails a saving throw, it can choose to succeed instead.

Acid and Poison Absorption. Whenever the Corrupter is subjected to Acid or Poison damage, it takes no damage and instead regains a number of hit points equal to the Acid or Poison damage dealt.

Uncanny Dodge. When an attacker that The Corrupter can see hits it with an attack,  The Corrupter can use it's reaction to halve the attack's damage against it.

Multiattack: The Corrupter makes five attacks from the choices below.

Bite. Melee Weapon Attack: +15 to hit, reach 5 ft., one target. Hit: (2d6 + 8) piercing damage + (2d6) acid damage

Claw. Melee Weapon Attack: + 15 to hit, reach 5 ft., one target. Hit: (2d8 + 10) slashing damage + (1d6) acid damage

Soul Blast (Counts as 2 attacks).  Ranged Weapon Attack: +14 to hit, range 20/60ft., one target. Hit: (3d10) necrotic damage and the target must make a Constitution saving throw (DC 21) or be stunned until the start of their next turn.

Cast a Spell. Costs 1 attacks to cast a Cantrip or 1st level spell, 2 attacks for a 2nd or 3rd level spell and 3 attacks for a 4th or 5th level spell. This can only be done once per turn.

Acidic Spikes. If the Corrupter takes damage from a melee attack, the attacker takes half of the damage they dealt to the Corrupter, half of this damage being piercing and the other half being acid damage.

The Corrupter has three legendary actions that it can use only at the end of another creature's turn. The Corrupter regains all spent actions at the start of it's turn.

Claw. The corrupter makes one claw attack.

Zoom. The Corrupter moves up to half it's speed

Cast a Spell (Costs 2 Actions).The Corrupter can cast one spell of 3rd level or lower, providing that it has the slots to do so.