When Arterial Alchemy enters, create a Blood token for each opponent you have. Blood tokens you control are Equipment in addition to their other types and have "Equipped creature gets +2/+0" and equip {2}.
2021-11-19
Blood tokens stop being Equipment if Arterial Alchemy leaves the battlefield. If any of them are attached to creatures at that time, they become unattached.
2021-11-19
If a Blood token is somehow both a creature and an Equipment, it can't be attached to a creature.
2021-11-19
If you control more than one Arterial Alchemy, creatures equipped with Blood Equipment will get +2/+0 for each Arterial Alchemy. The equip cost is still {2}.