Can Teemo, Swift Scout be played from hidden after damage is assigned and the battlefield is lost under the new control rules?

Ruling: No, you cannot play Teemo from hidden after losing the battlefield in combat. You need priority to play a hidden card, and once past the damage dealing step, there is no window to gain priority before the hidden card is trashed due to losing control of the battlefield.

Nuances:

• If a killed unit has a Deathknell effect that triggers after combat cleanup, there is debate about whether this creates a window to play the hidden card before it's trashed
• Rules As Written (RAW): Deathknell would trigger after special cleanup but before contested status is cleared, potentially allowing the hidden card to be played, though what happens after is unclear
• Rules As Intended (RAI): Hidden cards would be trashed before any triggers can enter the chain, so you would always lose the hidden card upon losing combat
• A Chinese referee FAQ clarified that control doesn't change until after all cleanups are complete, but whether chains can finalize before control changes is not clarified
• This represents a current gap in the rules; players should ask their head judge how they would rule it