Does Darius, Hand of Noxus add an unexhausted rune to the rune board, or does he generate 1 energy to help pay for a card's cost?

Ruling: Darius generates one energy (like tapping a rune) that contributes to paying for a card, but only after you've already played at least one card this turn. He does not lower the cost of the card itself, nor does he add a rune to the rune board.

Sequence:

• Play at least one card during your turn
• Then you can use Darius to generate one energy
• Use that energy to contribute to the payment of another card

Nuances:

• "Add" means contributing to the payment, not lowering the cost (this distinction may matter if future cards trigger off cost reductions)
• This is different from "Channel" which adds a rune from the rune deck to the rune board
• Because Darius has "add" on his ability, it can be used as part of playing another ability
• Darius cannot be used to accelerate Kai'Sa if she's your first card, since his ability requires playing at least one card first