Transmute is the keyword ability of cards in Ravnica block aligned with the Dimir guild.  It works by allowing a player to pay the transmute cost of a given card, discarding the card, then searching his or her library for a card with the same converted mana cost as the discarded card. It appears only on Black and Blue cards.
From the Comprehensive Rules:
- 702.52. Transmute
- 702.52a Transmute is an activated ability that functions only while the card with transmute is in a player’s hand. “Transmute [cost]” means “[Cost], Discard this card: Search your library for a card with the same converted mana cost as the discarded card, reveal that card, and put it into your hand. Then shuffle your library. Play this ability only any time you could play a sorcery.”
- 702.52b Although the transmute ability is playable only if the card is in a player’s hand, it continues to exist while the object is in play and in all other zones. Therefore objects with transmute will be affected by effects that depend on objects having one or more activated abilities.
- If you transmute a card with mana cost , for example, you can search for any card in your library with converted mana cost 2. It doesn't matter what type or colors that card is.
- You don't need to have another card with the same converted mana cost in your library to play the transmute ability, and you don't need to find a card even if there is one.
- Muddle the Mixture -
Counter target instant or sorcery spell.
Transmute (, Discard this card: Search your library for a card with the same converted mana cost as this card, reveal it, and put it into your hand. Then shuffle your library. Transmute only as a sorcery.)
 Color percentages
There is a total of 14 cards that involve transmute, which divide by color as such:
- Black = 36 %
- Blue = 36 %
- Multicolor = 21 %
- Land = 7 %