Decaying Touch - Kibble's Tasty

You wreath your hand in necrotic decay that causes anything you touch to wither and die. Make a melee spell attack against the target. On hit, the targets takes 1d6 necrotic
damage is starts to flake and decay. The first time they take damage from another source before the start of your next turn, they take an additional 1d6 necrotic damage. Targets immune to diseases are immune to this effect.

The both the initial and secondary damage of the spell increases by 1d6 when you reach 5th level (2d6), 11th level
(3d6), and 17th level (4d6).