Conjure Fiendish Butler V.S

Uttering a forbidden incantation, you summon a fiend from the lower planes. You choose a large or smaller challenge rating 15 or lower, such as a Green Abishai,  Nycaloth, or a Erinyes. The fiend appears in an unoccupied space that you can see. When it appears it is forced to make a charisma saving throw against your spell Dc. On a success, the spell fails expending the spell slot. On a fail, the creature willingly obeys all non-harmful commands becoming your personal combat maid. The creature can't use any legendary action or resistances and attempting to cast this spell is straining to the mind regardless of whether the spell is a success or failure you lose 2 from your wisdom score.

additional benefits

- can only be dispelled when casting this spell again, a level 9 dispel magic, or a similar effect

- while under this spell the creature's home plane is the same as yours and when the creature would die, it instead falls unconscious and remains so for 4 of its next turns before it can receive healing. during the turns it is unconscious it makes death saving throws, after three fails the creature dies and is no longer under your control. (only count fails)