What about the Death Knight Rune System?

Unlike other classes that use mana, rage or energy, Death Knights use a completly new “rune system” for their power.

• There are 6 runes, 2 blood runes, 2 frost runes, and 2 unholy runes
• When a rune is used it takes 10 seconds to be recovered
• When a rune is used you also power up another bar called your “runic power”. This runic power can then be used for other abilities.