Oni

The monster regains Hit Points at the start of each of its turns if it has at least 1 Hit Point.

The monster makes two Claw or Nightmare Ray attacks. It can replace one attack with a use of Spellcasting.

Melee Attack: +7 to hit. reach 10 ft. Hit: 1d12 + 4 slashing plus 2d8 necrotic damage.

Ranged Attack: +5 to hit. range 60 ft. Hit: 2d6 + 2 psychic damage.

The monster shape-shifts into a Small or Medium Humanoid or a Large Giant, or it returns to its true form. Other than its size, its game statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed.

The monster casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability: 1/Day Each: Charm Person (level 2 version), Darkness, Gaseous Form, Sleep

The monster casts Invisibility on itself, requiring no spell components and using Charisma as the spellcasting ability.

A creature you touch has the Invisible condition until the spell ends. The spell ends early immediately after the target makes an attack roll, deals damage, or casts a spell. Using a Higher-Level Spell Slot. You can target one additional creature for each spell slot level above 2.

One Humanoid you can see within range makes a Wisdom saving throw. It does so with Advantage if you or your allies are fighting it. On a failed save, the target has the Charmed condition until the spell ends or until you or your allies damage it. The Charmed creature is Friendly to you. When the spell ends, the target knows it was Charmed by you. Using a Higher-Level Spell Slot. You can target one additional creature for each spell slot level above 1.

For the duration, magical Darkness spreads from a point within range and fills a 15-foot-radius Sphere. Darkvision can't see through it, and nonmagical light can't illuminate it. Alternatively, you cast the spell on an object that isn't being worn or carried, causing the Darkness to fill a 15-foot Emanation originating from that object. Covering that object with something opaque, such as a bowl or helm, blocks the Darkness. If any of this spell's area overlaps with an area of Bright Light or Dim Light created by a spell of level 2 or lower, that other spell is dispelled.

A willing creature you touch shape-shifts, along with everything it's wearing and carrying, into a misty cloud for the duration. The spell ends on the target if it drops to 0 Hit Points or if it takes a Magic action to end the spell on itself. While in this form, the target's only method of movement is a Fly Speed of 10 feet, and it can hover. The target can enter and occupy the space of another creature. The target has Resistance to Bludgeoning, Piercing, and Slashing damage; it has Immunity to the Prone condition; and it has Advantage on Strength, Dexterity, and Constitution saving throws. The target can pass through narrow openings, but it treats liquids as though they were solid surfaces. The target can't talk or manipulate objects, and any objects it was carrying or holding can't be dropped, used, or otherwise interacted with. Finally, the target can't attack or cast spells. Using a Higher-Level Spell Slot. You can target one additional creature for each spell slot level above 3.

Each creature of your choice in a 5-foot-radius Sphere centered on a point within range must succeed on a Wisdom saving throw or have the Incapacitated condition until the end of its next turn, at which point it must repeat the save. If the target fails the second save, the target has the Unconscious condition for the duration. The spell ends on a target if it takes damage or someone within 5 feet of it takes an action to shake it out of the spell's effect. Creatures that don't sleep, such as elves, or that have Immunity to the Exhaustion condition automatically succeed on saves against this spell.