Traps

Traps are a sub-type of artifacts.

Traps must first be set and cannot be summoned the turn they are set. You do not need to disclose the that set artifacts are Traps.

Traps have one or more trigger-type effects, and once set, it can only be summoned when one of them would proc. Resolve the one effect being triggered (and only one), and then destroy the Trap.

Traps have the same special rule as Scrolls 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.