If I use Charm to move an opponent's unit into a battlefield where my Deadbloom is alone, does this trigger Master Yi's 'defend alone' ability?

Ruling: Yes, this triggers Master Yi's defend alone ability. The charmed unit is considered the attacker because it is the unit applying contested status to the battlefield.

Sequence:

• You charm the opponent's unit into the battlefield
• The moved unit applies contested status
• Since the moved unit's controller is your opponent and they are applying contested, they are the attacker
• Your unit (Deadbloom/Master Yi) is defending alone

Nuances:

• This works the same way for any forced movement effect (Ahri passive, Blitzcrank pull, etc.) - the unit being moved is always the one applying contested status and is therefore the attacker, regardless of how they got there