If Sivir, Battle Mistress Legend recycles a rune and exhausts herself to gain the gold gear token, then kills a unit like with Challenge, can she exhaust herself again after readying, or does she need to recycle another rune beforehand?

To answer your question: Yes, you must recycle another rune to exhaust Sivir, Battle Mistress again.

Here is the breakdown based on the game's mechanics:

1. Understanding the Trigger

Sivir’s ability is a triggered ability: "When you recycle a rune, you may exhaust me to play a Gold gear token exhausted."

• The trigger condition is "When you recycle a rune."
• Every time you want to exhaust Sivir to play the token, you must satisfy that trigger condition again by recycling a rune.

2. Why you cannot exhaust her twice for one recycle

When you recycled the first rune, that event happened, and Sivir's trigger condition was met. You then chose to place that instance of the ability on the chain and exhausted her to resolve it.

Even though she readies after an enemy unit dies, that readying effect does not retroactively "reset" or re-activate the previous recycle event. To exhaust her a second time, you need a new recycle event to occur to satisfy the "When you recycle a rune" trigger condition again.

3. The Sequence

To exhaust her a second time, the flow must look like this:

1. Recycle Rune A: Sivir’s ability triggers.
2. Exhaust Sivir & Pay Cost: You resolve the trigger to play a Gold gear token. Sivir is now exhausted.
3. Enemy Dies: An enemy unit dies (e.g., via Challenge). Sivir's second ability ("When one or more enemy units die, ready me") triggers. Sivir readies.
4. Recycle Rune B: You recycle a second rune. This creates a new trigger for Sivir.
5. Exhaust Sivir Again: You can now exhaust her again to play another Gold gear token.

Important Rules Context:

• Triggered Abilities: As defined in the Unleashed update, triggered abilities require their specific condition ("When you recycle...") to be met to be placed on the chain.
• Exhaustion Limits: Per Rule 414.1.b, an exhausted unit cannot be exhausted again, and Sivir only readies when the specific "enemy unit dies" condition is met. Simply readying her does not grant her an "extra" activation; she is just waiting for the next time her specific trigger condition is fulfilled.

Disclaimer: This is my interpretation based on the mechanics of triggered abilities and standard Riftbound rules. No official FAQ exists for this specific interaction.