Coppélia

Question : If my opponent controls a card such as Robin Hood that affects the cost of Characters when Coppélia is supposed to be played "for free", will I need to pay mana?

Answer : Coppelia is played for free! Playing a card for free means bypassing its cost entirely, which is different from reducing it to zero.

Question : Does Coppelia gain Fleeting when played for free via her effect?

Answer : Yes, unless something else prevents it, a card played for free follows the other rules, such as becoming Fleeting when played from Reserve.

Question : If Coppelia is played for free thanks to a Quick Action, such as the power of Treyst & Rossum, does it end the turn?

Answer : No. If the resolution of Quick Action includes playing a card, the turn continues normally.

Question : If another effect somehow sends Coppelia to the discard pile after she joins the Reserve from hand but before she's played, can she be played from discard?

Answer : In general, effects and abilities which affect a card when it's in a specific zone cannot track it if it changes zones unless they specifically mention this zone change. When Coppelia goes to Reserve from hand, her effect can find her in Reserve to play her because it specifically mentions this possibility, and it can find her in the Expedition zone to give her Asleep because, again, its effect mentions playing her. However, no part of the effect refers going to the discard pile (unlike a Moonlight Jellyfish which mentions "When I'm sacrificed") so it cannot find the card in the discard to play it.