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Lacerate Flesh deals 4 damage to target creature. Create a number of Blood tokens equal to the amount of excess damage dealt to that creature this way. (They're artifacts with "{1}, {T}, Discard a card, Sacrifice this token: Draw a card.")
If an effect refers to a Blood token, it means any artifact token with the subtype Blood, even if it has gained other subtypes.
Some spells that instruct you to create a Blood token require targets. You can't cast these spells without choosing all required targets, and if all of those targets become illegal targets, the spell won't resolve and you won't create any Blood tokens. If some but not all of those targets become illegal, you'll do as much as possible, including creating Blood tokens.
Some triggered abilities trigger "whenever you sacrifice a Blood token." These abilities trigger regardless of why you sacrificed that Blood token.
You can't sacrifice a Blood token to pay multiple costs.
A creature has been dealt excess damage if Lacerate Flesh deals more damage to it than the minimum amount of damage required to be lethal damage. In most cases, this means damage greater than the creature's toughness, but take into account any damage that was already dealt to it that turn.
