Death Spider

Your touch inflicts a curse which causes one of the target’s hands, feet, or a similar appendage to transform into a grotesque, hairy black spider that immediately begins consuming its host. A target must make a Dexterity saving throw to avoid the effect. 

On a failed save, the target’s limb is transformed and anything worn or carried by that limb drops away. The target takes 1d4 piercing damage at the start of each of its turns. If a hand is affected, the target can no longer hold anything with two hands and can hold only a single object at a time. If a foot is affected, the target’s speed on foot is halved, and they must use a cane or crutch to move. They also fall prone after using the Dash action, and have disadvantage on Dexterity checks made to balance. 

The afflicted limb may be severed and burned to destroy the death spider. If this is done before the start of the caster’s next turn, only a hand or foot will be lost. Afterwards, the entire limb will need amputation. A creature takes 4d12 slashing damage from losing a limb in this way. A remove curse spell ends the effect without incurring any damage. Magic such as the regenerate spell can restore the lost appendage. 

The target loses consciousness after 4 hours. If left unchecked, the death spider will inexorably consume its entire host by the end of the spell, at which point it turns into a giant spider.