You may have noticed the colored symbols around the mana costs of some Death Knight cards. These are called Runes. There are three Runes, one for each Death Knight spec: red is Blood, blue is Frost, and green is Unholy. These Runes dictate which Death Knight cards can be added to your deck during deckbuilding.

When building your deck, you select a combination of three Runes, which determines which Death Knight cards you can add to your deck. You can choose to fully devote to one Rune (such as triple Blood) or you can go primarily into one Rune, while dipping into another (such as double Unholy, single Frost). This Rune system allows for incredibly varied and powerful Death Knight cards, while making sure any particular deck isn’t just the best at everything. Instead, each of the Runes specializes in certain types of cards and effects.