There are still a lot of Generation 6 Pokmon from Kalos, where Mega Evolutions were first introduced, not in the game
Duplicates counted at a dining table can also change the selling plan
Add to that the shift cost to get Elsa in two turns earlier, and you can see why she froze out the competition for so long
When it comes to using counterspells, it's better to use them to stop cards resolving on your opponents' side rather than keeping your own stuff safe
You can choose any Magic character that has ever appeared in any official product or story, including characters that have appeared only in art
They're not skipped until they would begin, so if Trouble in Pairs leaves the battlefield before that happens, the extra turns will be unaffected