If the only enemy unit at a battlefield has Deflect when Ahri engages in combat, must you pay the 2 power to target it, or can you choose not to trigger the ability?

Ruling: You must pay the Deflect cost. Triggers are currently treated like Spells, and Spells don't have the option to NOT pay costs - only if you CAN'T pay costs does the ability not resolve.

Sequence:

• Ahri's attack trigger goes on the stack
• You can react to Ahri's attack trigger to float energy before the trigger resolves
• When Ahri's trigger resolves and you target the Deflect unit, you must pay the Deflect cost
• You can use any reaction add effects whenever you need to pay costs (special rule)

Nuances:

• If you literally cannot produce the power to pay for Deflect, you still must choose the Deflect target but the trigger whiffs
• Triggers are getting reworked, so this ruling might change in the future