The Painted World vs Delve Too Deep: Whenever a card leaves play, any lasting or delayed effects affecting the card while it was in play expire (see Leaves Play, RR, page 14). That includes The Painted World being treated as a copy of another card; as soon as The Painted World leaves play, it ceases to be a copy and goes back to just being The Painted World. Since the victory display is an out of play area, you could play The Painted World as a copy of Delve Too Deep, but as soon as it got added to the victory display it would cease to be a copy of Delve Too Deep and would go back to being The Painted World, thus losing its victory points.

The Painted World vs Fast cards (such as Elusive or Ward of Protection): The Painted World is "played as a copy” of an event, which means if that event is fast, The Painted World will also be fast, and if that event has a play restriction or trigger (like “Play after blah blah blah”), The Painted World would also have that same restriction or trigger if played as a copy of that event.

Q: Can you use Uncage the Soul on The Painted World when it's copying a non-Spell-traited card under Sef? A: You can use Uncage the Soul to play The Painted World from your hand (regardless of whether or not the card you are copying has the Spell trait). Uncage the Soul allows you to play a Spell or Ritual card from your hand, reducing its resource cost by 3. Since The Painted World is still a Spell at the time you are choosing a card to play using Uncage the Soul, you can choose The Painted World as its target. Then, as soon as you begin the sequence of actually playing the card (including checking play restrictions and determining the card’s cost) The Painted World becomes a copy of whatever card you are choosing to play it as (in this case, Hot Streak or Backstab or whatever other card you want to copy).

Q: How does The Painted World interact with Crystallizer of Dreams, as they both replace the discard effect? A: "Both effects are replacement effects, and since The Painted World’s replacement effect is forced and Crystallizer of Dreams is optional, the forced effect would take priority and resolves first. Therefore The Painted World must be removed from the game after it is played and cannot be placed underneath Crystallizer of Dreams."

Q: Double, Double vs The Painted World. I imagine The Painted World cannot be played twice by Double, Double, since it's removed from the game, but can the copied event be played twice? A: You can absolutely use Double, Double to play The Painted World twice. Note that it says you play it “as if it were in your hand,” so each time you played it in this way, you could choose a different event beneath Sefina Rousseau. Keep in mind this may not work with some events (such as events that become attachments or go to a specific play area) as you only actually have one physical copy of The Painted World to move around. UPDATE: There is an extant ruling that one can trigger Double, Double after playing The Painted World (and target different cards no less). A recent ruling said that one cannot trigger double double after playing Cheat Death as Cheat Death will have been removed from the game as part of its resolution. As The Painted World is also removed from the game during its resolution (albeit with slightly different timing) is this ruling no longer valid? Would the same be true of any card removed from the game? A: Under current rulings, removing The Painted World from the game is a part of its resolution, so it would be an ineligible target for Double, Double. This does overrule the previous ruling.