Scroll

Scrolls are a sub-type of artifacts.

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

They have a special rule regarding their Knowledge Stat: unlike other cards, they do not acquire Mana counters when summoned; in fact their "mana" is considered "spent" when their effect activate. However, their can still be sac'ed face-down to acquire a discount from Hidden Knowledge. Do note that, if you choose to do so, you can't also use the same Scroll as a artifact or generic card sac cost.