When Hook kills Ekko and reveals another Ekko from the top of the deck, can you use the first Ekko's deathknell runes to pay for the second Ekko's accelerate cost?

Ruling: No, you cannot pay for the revealed Ekko's accelerate cost with the killed Ekko's deathknell runes. The revealed Ekko will be played before the deathknell resolves.

Sequence:

• Hook kills Ekko, triggering its deathknell (goes to pending chain)
• Hook reveals Ekko from top of deck (goes to pending chain)
• First Ekko's deathknell is finalized and goes on the chain
• Second Ekko is finalized and plays immediately (because it's a permanent)
• First Ekko's deathknell resolves from the chain

Nuances:

• The order in which items are added to the pending chain doesn't matter in this case, because permanents are played immediately when finalized, while triggered abilities go on the chain to resolve later