Can I react to my Lonely Poro deathknell trigger with Vilemaw?

Yes, you can react to your Lonely Poro's Deathknell trigger by playing Vilemaw.

Why this works:

1. Chain State: When Lonely Poro dies, its Deathknell trigger is added to the chain. This puts the game into a "Closed" state, which allows players to play [Reaction] cards (or units with [Ambush], as Vilemaw has).
2. LIFO Resolution: The chain resolves in Last-In, First-Out (LIFO) order. When you play Vilemaw in response, it is placed on top of the Deathknell trigger on the chain.
3. Historical Check: According to RiftJudge FAQ #9841 and FAQ #10756, the Lonely Poro's "alone" condition is a historical check. The game evaluates whether it died "alone" (no other friendly units present) at the moment of its death. Because this condition was satisfied at the time of death, the arrival of Vilemaw later in the chain does not retroactively invalidate the trigger.

Sequence of Resolution:

1. Death Event: Lonely Poro dies while alone at the battlefield. The Deathknell trigger is created and added to the chain.
2. Reaction: You play Vilemaw using its [Ambush] keyword in response to the Deathknell trigger. Vilemaw is added to the top of the chain.
3. Resolution:
   • The chain resolves LIFO. Vilemaw enters the battlefield first.
   • Lonely Poro's Deathknell trigger resolves second. Since the "alone" condition was already met at the moment of death, you successfully draw 1 card.

Note: This interpretation is based on established FAQs regarding the historical "alone" check for Lonely Poro.