Bank

Bank is a keyword ability that allows a player to save up a card for a next game within a match. The mechanic appeared on a test card in the Mystery Booster set.

Description
If a card with Bank is cast from your hand, it is exiled until the end of the match. The player may cast it from exile during another game during the match. It still counts towards the deck minimum.

This might be interesting for a Control player, which can have a weaker game one in a lot of matchups. After sideboarding, game two can be played with an added advantage. It also makes the deck more efficient by making it one card smaller, but still counting.

Rulings

 * If a card with bank doesn't resolve for any reason (such as being countered, or all of its targets becoming illegal if it has any), it won't be banked.
 * Banked cards begin the next games in a match in exile. They're not outside the game.
 * Once you cast a banked card from exile, it behaves like any other spell. It may be countered, and it'll be put onto the battlefield if it resolves as a permanent spell, or into its owner's graveyard if it's not a permanent spell.
 * If you cast a spell you don't own or gain control of a spell, you didn't cast it from your hand, so you don't bank it.