Does Darius's effect 'When you play second card get +2 and ready' trigger when he is in hand or champion slot, or does he have to be in play?

Ruling: Darius must be in play for his effect to be active. His effect triggers when you play your second card in a turn, regardless of whether Darius himself is the first or second card played.

Sequence:

• If you play Darius first, then play another card, Darius will trigger (he is in play when the second card is played)
• If you play another card first, then play Darius, Darius will trigger (he is the second card played)

Nuances:

• A card in hand cannot be ready or exhausted, so Darius's ready effect only applies when he is already in play