Contract of Life and Death

You use your life as a resource to channel dark magic into an agonizing bolt of energy. make a ranged spell attack against a creature in sight. Pick between 1-20, you take that much necrotic damage, and resistance/immunity doesn't affect the damage in any way, meaning the damage is still dealt to you. You shoot a bolt of 1-20d4 depending on the number of necrotic damage you choose to take. More so, the number of damage also applies a secondary effect:

10-15: The target's speed is reduced by half until the start of your next turn

16-20: If the damage reduces the creature to 0hp the creature becomes a ghoul under your control for 1d10 hours.