Dark Confidant and split cards
If it's somewhere other than on the stack or if it's fused, a split card's CMC is the sum of each half's CMC.

708.4. In every zone except the stack, the characteristics of a split card are those of its two halves combined. This is a change from previous rules.
708.4b The mana cost of a split card is the combined mana costs of its two halves. A split card’s colors and converted mana cost are determined from its combined mana cost.
Example: Assault/Battery’s mana cost is {3}{R}{G}. It’s a red and green card with a converted mana cost of 5.  If you cast Assault, the resulting spell is a red spell with a converted mana cost of 1.

708.4b is rather poorly worded. As the example shows, the mana cost and converted mana cost of a split card is only the combined mana costs or converted mana costs of its two halves when it's not on the stack or when it's fused.