Aracnomorph

You target a creature with range, who must make a Charisma saving throw. On a success, nothing happens and the spell ends. On a failure, one of their appendages of your choice magically polymorphs into a spider that is attached to their body. If the appendage is being used to hold something, that thing is dropped. If the appendage is necessary for the creature's movement, the creature's speed is halved. If the appendage is used for an attack, such as a tail, or claw attack, that attack is impossible for the duration of the spell.

The spider has 20 HP and an AC of 12. While the spider is alive, the creature takes 2d6 piercing damage at the start of their turns. If the spider dies, the spell ends and the spider turns back into the limb. If the creature dies while the spider is still alive, the spell ends, and the spider detaches and becomes a giant wolf spider permanently under your control.