When Yasuo is moved to an occupied battlefield by an opponent's effect (like Blitzcrank), does Yasuo become the attacker or defender, and does his ability trigger?

Ruling: Yasuo is always the attacker when moved to an opponent's occupied battlefield, regardless of who controls the effect that moved him. The attacker is determined by whose unit applies the contested status to the battlefield. His ability triggers whenever he is moved to a battlefield occupied by an opponent.

Sequence:

• Yasuo is moved to an opponent's occupied battlefield
• Yasuo becomes the attacker (applies contested status)
• Yasuo's ability triggers
• The ability resolves (unless Yasuo dies or moves out before resolution)

Nuances:

• If Yasuo dies or moves out before his ability resolves, the ability still resolves but has no effect ("fizzles")
• This can work against you: if there is only one defender with Deflect at the battlefield, you are forced to target them with Yasuo's effect and pay a Power