They need to make a profit reselling the cards, so youre paying for the convenience of instant payment
As Interceptor returns to the battlefield because of its triggered ability, you choose which player, planeswalker, or battle it's attacking
There doesnt seem to be a timer built in but it would make sense for competitive play if there is already a pause button
Remember, this determines a lot about what the final creature is including power and toughness, the name, and the creature type
Any updates will be posted before the Prerelease events start on July 26 and the global launch on Aug
Its also a really fun card, letting you control a rivals card, but with it being cheaper depending on how much more powerful that card is