Tainted Strike

For the duration of the spell, your arm and anything you are holding gets coated in Phyrexian Oil, which forms a claw shape around your arm. It can be molded with your mind into any shape of up a foot by foot by foot cube. Whenever any creature not aliened with Phyrexia including you comes in contact with it, they make a DC 13 con saving throw. On a failed throw, the target takes 4d4 necrotic damage immediately and an additional 2d4 necrotic damage at the start of each of its turns for as long as it is in contact with the oil. The target takes half that much damage on a successful throw, and no additional damage. Whenever a creature in contact with the oil begins their turn, they may make a DC 17 Con saving throw to remove the oil. Additionally, a creature may spend an action to take an additional con saving throw or a DC 21 strength saving throw. If a creature dies while in contact with the oil, they get a failed saving throw at the beginning of their turns, cannot be healed by any magic, and if they die the DM rolls a D20 each turn they would have instead of dying normally. On a 10 or lower, the infected creature returns to half health temporarily as an Undead minion to Phyrexia. 

Minion to Phyrexia A minion to Phyrexia has only one goal: To spread the Phyrexian glory and infect as many creatures as possible to the best of its ability. It might try to coat its weapons with the oil or unite with other minions.