Venuraya's Entropic Leech

You point at one creature you can see within range, that has been previously wounded and currently has less than its maximum HP. Make a ranged spell attack against that creature. On a hit, the target immediately takes 3d10 necrotic damage as their own blood begins to be magically withdrawn from all open wounds. While under the effect of this spell, the target's base movement speed is halved as they struggle to control their own body.  There is no save against the initial ranged spell attack effect.

Once you begin to exsanguinate your target, you merely have to maintain line of sight and focus on the manipulation to cause damage. On each of your turns for the duration, you can concentrate your grisly exploitation and extend the effects. The target may make a Constitution Saving Throw each turn that you choose to maintain the spell.

On each subsequent round after the initial spell attack hits, the caster may deal an additional 3d10 necrotic damage to the target as their standard action. The target may make a Constitution saving throw against the spell DC at this time.  If the target succeeds they take half damage and all effects end immediately after inflicting the halved damage as the target regains control of their body.  If the target fails the save they take the full damage. The target may reattempt the saving throw each turn that you attempt to withdraw blood.

As the blood is drawn out, it is immediately evaporated into a transparent vapor upon contact with the open air, and is effectively destroyed.There is no trail of blood left behind as it is destroyed magically. Blood destroyed in this manner cannot be used for blood magics or necromantic healing of any sort- it simply ceases to exist.

This spell may be maintained for up to 1 minute of concentration before the manipulation of blood magic becomes unstable.  The spell otherwise ends if you use your standard action to do anything else, or if the target succeeds on the saving throw, or has total cover from your sight. If the target dies while you are concentrating on this spell the spell ends immediately and cannot be transferred to a different target.

At Higher Levels. When you cast this spell using a spell slot of higher level, the damage increases by 1d10 for every level above 3rd.(ie. initial damage begins at 3d10 at third level, 4d10 at fourth level, 5d10 at fifth level, etc.)