Bone Rot

you can rip the moisture and nutrients from the bones of one creature that you can see within range. That creature must make a con saving throw or have their bones weakened. the affected target takes 1d4 necrotic damage and for every 5ft they move in a turn they take more necrotic damage equal to your spellcasting mod. The effected target can reroll their save at the end of each of their turns, the effect lasts for 5 rounds or until they succeed on their saving throw.

at 5th lvl: the initial damage increases to 2D4 damage, 3D4 at 11th lvl, and 4D4 at 17th.