When Ekko dies and triggers Deathknell with Karthus on the field (which doubles triggers), can you ready your runes twice, or does the recycle cost prevent this?

Ruling: You cannot ready your runes twice from a single Ekko dying with Karthus on the field because Ekko's "recycle me" is a mandatory cost paid at resolution, and you cannot recycle Ekko twice. However, if you have two Ekkos on the field, you can ready runes between each Deathknell trigger resolving.

Sequence:

• When Ekko dies, Deathknell triggers enter the chain
• You can tap runes for energy in response before triggers resolve
• When each Deathknell resolves, you must recycle that Ekko to ready your runes
• You can tap runes again between resolution of different triggers

Nuances:

• The "recycle me to ready your runes" uses "[do X] to [do Y]" templating, making recycling a cost paid at resolution, not an upfront cost
• This cost is mandatory (not "may"), so you must recycle Ekko and ready your runes when the trigger resolves
• Karthus doubles the trigger, but the second instance still requires recycling the original Ekko, which is already recycled
• With multiple Ekkos dying, each can be recycled separately for their own trigger