Big Deep-Fryer

You touch a creature, and that creature must make a dc 21 Constitution saving throw or be deep-fried by your touch. Through the dark arts, the creature is now vulnerable to all forms of damage, no matter what damage resistances the creature had before for the duration of the spell. The target has a walking speed that is now 10 less than it had before. Upon getting touched, the target takes 10d4 fire damage as well as 10d4 necrotic damage. The target only takes half damage if it succeeds on it's saving throw. This spell can be dispelled using Greater Restoration. The damage increases by 2d4 fire damage and 4d4 necrotic damage for each level scaled upwards.