Athron Oni

Innate Spellcasting. The oni's innate spellcasting ability is Charisma (spell save DC 13). The oni can innately cast the following spells, requiring no material components:

At will: invisibility, darkness, mind sliver, intellect fortress

1/day each: Summon fiend (demon only), summon shadowspawn, hunger of hadar, Hold monster

Magic Weapons. The oni's weapon attacks are magical.

Regeneration. The oni regains 10 hit points at the start of its turn if it has at least 1 hit point.

Multiattack. The oni makes two attacks, either with its claws or its scimitar.

Claw (Oni Form Only). Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 4) slashing damage.

Scimitar. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) slashing damage, or 9 (1d10 + 4) slashing damage in Small or Medium form.

Change Shape. The oni magically polymorphs into a Small or Medium humanoid, into a Large giant, or back into its true form. Other than its size, its statistics are the same in each form. The only equipment that is transformed is its glaive, which shrinks so that it can be wielded in humanoid form. If the oni dies, it reverts to its true form, and its glaive reverts to its normal size.

Demonic rage. The whenever the oni changes shape all creatures within 10 ft take 1d8 psionic damage.

Psionic mastery. 1/day. As a bonus action, the oni can infiltrate into the targets mind. The target must succeed on a constitution saving throw with disadvantage. If successful the target takes 1 psionic damage and nothing else. If not, the oni gains control over it until it’s next turn.

Recoilment. 1/day. If the oni takes damage, it can choose to teleport anywhere within one mile.