If Hook kills a buffed Soaring Scout and tutors Karthus, does Scout's Deathknell trigger before or after Karthus enters the board?

Ruling: Karthus will not be on board before the Deathknell enters the chain. The Deathknell trigger will enter the chain first, then Karthus will be played.

Sequence:

• Hook kills Scout, Scout enters as pending
• Karthus is banished and begins being played, enters as pending on top of Scout
• Hook finishes resolving
• Scout is finalized and the Deathknell trigger enters the chain
• Karthus is finalized and immediately played
• Scout's Deathknell resolves

Nuances:

• Pending items are finalized in the same order they are put on the chain (which is opposite to how items on the chain resolve)
• Karthus was not on board before the Deathknell fully entered the chain, so it doesn't trigger twice