Gating

Gating is a term that refers to cards that require you to return a creature that shares a color with it to your hand when it comes into play in exchange for a lower casting cost. All gating cards printed are multicolored. Gating cards were introduced in Planeshift. Gating is not an ability or a keyword.

List of Gating cards:

Cavern Harpy Doomsday Specter Fleetfoot Panther Horned Kavu Lava Zombie Marsh Crocodile Natural Emergence

Razing Snidd Sawtooth Loon Shivan Wurm Silver Drake Sparkcaster Steel Leaf Paladin

The most powerful of these is the Shivan Wurm, a 7/7 trampler which could be cast third turn in a green deck with mana-producing creatures. Meanwhile, Fleetfoot Panther's gating cost can actually be a boon, as its flash ability can save a creature already in play from destruction.

Rulings

• Gating cards read "Whenever [this card] comes into play, return a [color A] or [color B] card to your hand." That's a triggered ability, so players can respond to it going on the stack by playing instants or activated abilities.
• Like any comes-into-play triggered ability, the gating ability will trigger regardless of whether the card comes into play from a player's hand, graveyard, or library (or any other zone).
• The gating triggered ability doesn't target anything, so it's perfectly fine to return an untargetable card you control (or a card with the right kind of protection) to its owner's hand.
• When the gating ability resolves, if you control no appropriate cards of the specified colors other than the gating card, you'll have to return the gating card itself to your hand. If the gating card turns out to be an invalid choice (for example, if you change the gating card's color before its comes-into-play ability resolves), then the gating ability does nothing.