Scroll

Scrolls are a sub-type of artifacts with a powerful, one-off, "When summoned:" trigger effect, and then are essentially clutter until they can be destroyed.

They have a special rule regarding their Will: unlike other cards, they do not acquire Mana counters when summoned; in fact their "mana" is considered "spent" when their effect activates. However, they can still be sac'ed face-down for their Will to count towards a mana cost via the Hidden Sacrifice rule, before they are ever flipped.