Blood is unlocked after defeating the Blood Wiz at level 1700. (After 1700 you will no longer gain a power from defeating a boss every 100 levels.) Upon defeating the Blood Wiz you will unlock the Blood tab. Inside the blood tab you will find 3 upgrades and a blood bar. The first upgrade is Speed. This upgrade increases how fast blood goes in to the machine by 2x (Multiplicative) . The second upgrade is Potency. This upgrade increases your blood gain from enemies on higher levels up to a cap of the Potency level, which goes up by increments of 0.01. The last upgrade is the Potency Cap. This upgrade increases the effectiveness of potency by 100 levels (which is additive with each level).