When Arterial Alchemy enters the battlefield, create a Blood token for each opponent you have. (It's an artifact with "{1}, {T}, Discard a card, Sacrifice this artifact: Draw a card.")
Blood tokens you control are Equipment in addition to their other types and have "Equipped creature gets +2/+0" and equip {2}.
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.
If a Blood token is somehow both a creature and an Equipment, it can't be attached to a creature.
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}.