Only Blood tokens controlled by the player Bloodvial Purveyor is attacking or the controller of the planeswalker it's attacking are counted to determine the bonus from its last ability.

If an effect refers to a Blood token, it means any artifact token with the subtype Blood, even if it has gained other subtypes.

You can't sacrifice a Blood token to pay multiple costs.

Some triggered abilities trigger "whenever you sacrifice a Blood token." These abilities trigger regardless of why you sacrificed that Blood token.