If an opponent controls red Darius and you play Possession to take control of him, does Darius see Possession as the first card played for his ability?

Ruling: Yes, Darius sees Possession as the first card played. When Possession resolves, you take control of Darius, and then when you play your second card, Darius triggers under your control.

Sequence:

• Possession is played as your first card
• Possession resolves, switching Darius to your control
• You play your second card
• Darius triggers because you (his new controller) have played your second card this turn

Nuances:

• Darius does not need to be under your control when the first card is played; he only checks that his controller has played their second card when a card is played
• Darius can trigger off being the second card himself using the same logic
• A card only counts as "played" once it has resolved, not when it's cast