When a unit with a Deathknell trigger (like Kog'Maw) dies, what is the timing for playing hidden cards or reacting to the trigger, especially regarding battlefield control and combat scenarios?

Ruling: There is no official answer to this timing question. The rules are not clear enough to definitively resolve where Deathknell triggers sit in the combat resolution sequence, particularly regarding when battlefield control changes and when hidden cards are trashed.

Debated Scenarios:

• Non-combat death (spell kills Kog'Maw): Most interpretations suggest the unit dies, battlefield control is lost, and hidden cards are trashed all in the same cleanup, giving no window to play the hidden card after death.
• Combat death with contested battlefield: Multiple conflicting interpretations exist about whether Deathknell resolves before or after conquering/scoring, and whether players retain control long enough to react.
• Combat death timing: Debate centers on whether Deathknell triggers resolve between damage and conquering (440.1.a vs 440.1.b vs 440.2), or only after the entire Resolution Step completes.

Nuances:

• If the battlefield becomes contested during combat, control cannot change while contested, but the exact timing of when contested status clears relative to Deathknell resolution is disputed.
• The rules around cleanup loops and when pending items finalize versus when they can be reacted to are unclear in this context.
• This is described as a "hot topic" with contradicting opinions and no consensus, awaiting official clarification from Riot.