Rakshasa

The rakshasa automatically succeeds on saving throws against spells and other magical effects, and the attack rolls of spells automatically miss it. Without the rakshasa's permission, no spell can observe the rakshasa remotely or detect its thoughts, creature type, or alignment.

If the rakshasa dies outside Gehenna, its body dissolves into ichor, and it gains a new body instantly and revives with all its Hit Points in Gehenna.

The rakshasa makes three Cursed Touch attacks.

Melee Weapon Attack: +10 to hit, reach 5 ft.. Hit: 12 (2d6 + 5) slashing plus 19 (3d12) necrotic damage. If the target is a creature, it is cursed. While cursed, the target gains no benefit from finishing a Short or Long Rest.

Recharge 5–6. Wisdom Saving Throw: DC 18, each enemy in a 30-foot Emanation originating from the rakshasa.
Failure: 28 (8d6) psychic damage, and the target has the Frightened and Incapacitated conditions until the start of the rakshasa's next turn.

1 use per day. The rakshasa casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 18):
At Will: Detect Magic, Detect Thoughts, Disguise Self, Mage Hand, Minor Illusion
1/Day Each: Fly, Invisibility, Major Image, Plane Shift