Does Nocturne have an optional additional cost that would be reduced by Purple Ezreal's ability?

Ruling: Nocturne does not have an optional additional cost. The power cost to play Nocturne from banish is just the regular cost you pay to play the card, not an additional cost.

Sequence:

• First, decide whether to banish Nocturne when you look it up or reveal it
• If you banish Nocturne, it goes to the banish zone (a public zone)
• Then decide whether to play Nocturne from banish
• If you choose to play it, you must pay the 1 power cost as its regular cost
• If you don't pay the cost, Nocturne remains banished

Nuances:

• Optional additional costs refer specifically to mechanics like Accelerate or Repeat, not alternative ways to play cards
• Alternative costs (like Immortal Phoenix or Flame Chompers) are also not optional additional costs
• The distinction matters for effects like Purple Ezreal that specifically reduce "optional additional costs"
• Banish zone is a public zone, so all players can see cards banished there