You fire a bolt of negative energy against one creature you can see within range. Make a ranged spell attack against the target. On a hit, a part of the target's body will necrose. The target takes 5d8 necrotic damage. Add your spellcasting modifier to the total necrotic damage. Then, the target is subjected to one of the following effects until the end of your next turn, based on the body part you hit (this is determined by the attack roll, as seen below.)
Roll successful by a margin of 1-3: You hit the enemy's left or right arm (your choice). They have disadvantage on weapon attacks and unarmed strikes, and wielding a two-handed weapon becomes impossible. If the affected arm holds a shield, the target loses that shield's AC for the duration. If the affected arm holds a weapon, they cannot wield it with that arm, and must switch arms or be incapable of wielding the weapon.
Roll successful by a margin of 4-6: You hit the enemy's left or right leg (your choice). They can only move 1/3 of their total movement speed, dashing or dodging is not possible and whenever they walk, they must make a Dexterity saving throw or fall prone. The save is made with disadvantage if the target is on difficult terrain.                                                                          Roll successful by a margin of 7 or more: You hit the enemy's chest. They feel immesurable pain, and are Stunned by it.
Natural 20: You fire a beam with increased power, directly at the target's head. They fall unconscious. They need not make death saves unless their health goes below 0, but they suffer all other penalties for being unconscious. Being healed does not wake them from this state.

If you desire an effect with a required margin lower than the one you rolled, you may choose it instead.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, you deal an additional 1d8 necrotic damage for each slot level above 4th. Additionally, if the slot is of 7th level or higher, the effect lasts for 8 hours (a lesser restoration spell or higher ends it immediately). If cast with a 9th-level slot, the effect lasts until dispelled.