When attacking with 2 Anivia into a battlefield with 2 Nocturnes and a hidden Teemo Strategist, when is the latest the defending player can flip Teemo before losing control of the battlefield due to all units dying to Anivia triggers?

Ruling: The defending player can wait until after both Anivia triggers resolve to flip the hidden Teemo Strategist. During a showdown, you maintain control of a contested battlefield even if you have no units remaining on it.

Sequence:

• Both Anivia triggers resolve, killing both Nocturnes
• Focus passes back and forth during the showdown as normal
• Defending player receives focus after the attacker uses or passes it
• Defending player can flip the hidden Teemo Strategist while still controlling the battlefield

Nuances:

• This rule changed in version 1.2 - previously cleanup would cause loss of battlefield control immediately
• As long as a battlefield is contested (during showdown), you don't lose control even with no units present
• You would only need a Deathknell trigger if you wanted to flip after the showdown completely resolves