You attempt to create a bond between your blood and that of a target creature within 30ft. The creature has to make a Constitution saving throw. On a fail, the target takes 3d6 necrotic damage and their blood becomes tainted with that of the user's, creating a bond. On a success, the creature takes half of the damage and no other effects manifest.

While this bond persists, you may cause the tainted blood to react violently from within the creature, interfering with their actions. When the infected creature makes an attack roll, ability check, or saving throw, you can use your reaction to agitate the tainted blood inside of them, causing them to have disadvantage on the triggering roll. Also, if you take damage from an effect as part of your own spell or ability, the infected creature takes the damage instead (Does not count for directly targeting yourself, such as hitting yourself with an Eldritch Blast).

You can only impose disadvantage to saving throws only if you can visually see the effect happening. (For example, you can visually see an explosion and its aftereffects, but not spells that involve reading/tampering a creature's thoughts.)

At the end of the infected creature's turn, they can attempt taking back full control of their body, making another Constitution saving throw. On a success, the effects of this spell end.