What if I cull the weak and both mine and enemy unit have deathknells? What is the order on the stack?

When you play Cull the Weak and both your unit and your opponent's unit have Deathknell abilities, they will die simultaneously when the spell resolves. Their Deathknell abilities will then trigger and be placed on the chain together.

According to Rule 376.3.b.1 and RiftJudge FAQ #9265, the order in which these triggers are placed on the chain is determined by the players, starting with the Turn Player.

The Sequence of Events:

1. Resolution of Cull the Weak: The spell resolves and kills both units simultaneously.
2. Triggering: Both Deathknell abilities trigger simultaneously.
3. Ordering on the Chain:
   • The Turn Player chooses the order for their controlled Deathknell triggers first, placing them on the chain.
   • The next player in turn order then places their Deathknell triggers on the chain.
4. Resolution (LIFO): The chain resolves in Last-In, First-Out order. This means the triggers added to the chain last (by the non-turn player, if applicable) will resolve first.

Summary: If you are the Turn Player, you place your triggers on the chain first, meaning your opponent’s triggers (placed after yours) will resolve first. If you are the non-turn player, your opponent places their triggers first, meaning your triggers will resolve first. If you control both units, you choose the order for both (as per FAQ #4235).