Curse of Harm

You channel malign energy to cause grievous harm to a humanoid creature within range. For the duration of the spell, the target suffers the effects from one of the curses listed below, depending on how you choose to complete the spell. The target makes a Charisma saving throw at the end of each of its turns. If the target succeeds on three saving throws, the curse immediately ends. These successes do not need to be consecutive, but if the target fails three saves in a row, they lose all recorded successes and must start again.

Blinding Curse. Dousing the doll in ink causes the target to lose the use of its senses, and watery ink begins to run from its ears, nose, mouth, and tear ducts, staining its eyes and tongue. The target is blinded and deafened for the duration of the curse, and it cannot use its sense of smell. If the target fails three saving throws in a row, roll a d4. The creature permanently losses the use of the senses determined by the result: 1) Sight ; 2) Hearing ; 3) Smell ; 4) Taste.

Burning Curse. Allowing the the doll to be consumed by fire causes the target to blister and burn. The target suffers 8d6 fire at the beginning of each of its turns for the duration of the curse. If the target fails three saving throws in a row, they are engulfed in flames that shed bright light in a 20 ft. radius and dim light for 20 ft. beyond that. These flames inflict a further 2d6 fire damage at the end of each of the target's turns, and cannot be extinguished by non-magical means so long as the curse remains in effect.
If the target is on fire when the curse ends, the flames remain. However, the burning creature may extinguished with fire with a DC 10 Dexterity saving throw, or by any other reasonable means.

Choking Curse. Holding the doll completely underwater or burying it in earth or sand causes the target to suffocate for the duration of the spell, as their lungs, throat and mouth are filled with the material the doll is submerged in. When the curse begins, the target is considered to be holding its breath. It may do so for a number of minutes equal to 1 + its Constitution modifier (minimum 30 seconds) before it begins to choke. A choking creature can survive for a number of rounds equal to its Constitution modifier (minimum 1), before dropping to 0 hit points. If the target fails three saving throws in a row it immediately begins choking if it is still holding its breath, or immediately fall to 0 hit points if it is already choking. The curse immediately ends if the target drops to 0 hit points. 

Decaying Curse. Allowing the doll to be consumed by acid causes the target to burn, and inflicts the ravages of decay upon their equipment. The target suffers 4d8 acid damage at the start of each of its turns for the duration of the curse. If the target fails its saving throw, any non-magical armour it's wearing is subject to a permanent -1 penalty to its AC. If this reduction would reduce its AC to 0, the armour is destroyed. If the target fails three saving throws in a row, roll a d4. One randomly selected non-magical weapon that it is carrying suffers a permanent penalty on attack and damage rolls equal to the amount rolled. If the reduction would be sufficient to render it useless, the weapon is destroyed.
At the DM's discretion, this affect may afflict non-magical musical instruments or spellcasting foci if the cursed creature is not holding an applicable weapon.

Freezing Curse. Plunging the doll into freezing conditions causes the target to feel the sudden bite of winter in its veins. The target's speed is halved and it has disadvantage on Dexterity saving throws for the duration of the curse. If the target fails its saving throw, it may take either an action or bonus action on its next turn, but not both. If the target fails three saving throws in a row, their body becomes encased in a layer of ice: their movement speed is halved again, and they automatically fail any Dexterity saving throws.

At the DM's option, you may choose an alternative curse effect, but it should be no more powerful than those described above. The DM has final say on such a curse's effect.