Conjure Rot Grub

At the completion of casting this spell, you must spend a hit die. If you do, you summon a Rot Grub which takes up immediate residence inside your body. While the Rot Grub is inside of you, you gain access to the following bonus action:

Infect with Rot Grub: Make an unarmed melee attack; reach 5 ft. or your normal reach, one target. When you hit with this attack, the target must succeed on a constitution savings throw with a DC equal to your spell saving throw value or become infected with Rot Grubs.(1d6 necrotic damage at the start of the creature's turn and must succeed on a DC12 Con save or the infection worsens by +1d6 and +2 DC; if the target fails this save on three consecutive turns they die and become a zombie at the start of the next turn) This damage ignores resistances and ignores the target's immunity to necrotic damage, but only deals 1/2 damage.

Can be cast at higher level and the DC and number of d6 used when figuring damage increase by 1 for each slot level above 1st.