Blood to Sand

You point at one creature that you can see within range and attempt to transform the blood inside their body into withering sand. That creature must make a Constitution saving throw. On a failed save, the target takes 8d6 necrotic damage and 8d6 slashing damage as the flow of sand begins to slash through their veins until the spell ends. On a successful save, the target takes half damage and does not incur the following effects.

At the start of each of its turns, while sand courses through the target's body, it takes 8d6 necrotic damage, 8d6 slashing damage, and becomes poisoned until the end of its next turn. While poisoned in this way, it is incapacitated.

A creature withering into the embrace of the desert must make another Constitution saving throw at the end of each of its turns. If it successfully saves against this spell three times, the spell ends. If it fails saves three times, it instantly takes 8d6 necrotic damage, the spell ands, and the transformation becomes permanent. The magical effect lingers inside the target's body. It will be incurably poisoned and take 8d6 slashing damage at the start of each of its turns until it dies. The success and failures do not need to be consecutive; keep track of both until the target collects three of either.

A dispel magic spell can end the permanent effect only if it is cast as a 9th-level spell. Creatures that do not have blood are immune to this spell. A creature who dies while affected by this spell or by the permanent magical effect turns completely to sand.