Can I reveal a hidden Teemo after Kog'Maw's Deathknell triggers to keep control of the battlefield, or must I reveal it before Deathknell triggers?

Ruling: This is an unresolved rules interaction with no official answer. The community has identified three possible interpretations, and players should ask their judge which interpretation is being used at their event.

Nuances:

• One interpretation: If you can insert a chain between combat and control changing, another combat will be staged in the cleanup after the unit enters the board
• Second interpretation: Control is lost before deathknells finalize, preventing the play
• Third interpretation: Playing the unit would be an illegal action that must be undone
• You can always flip Teemo before combat damage is dealt to avoid this rules uncertainty
• An official ruling from Riot is needed to resolve this interaction