2. Tracking for the former shapeshifters
Some cards, like the new Band of Misfits, can play a card that isn't put into play. When you play Band of Misfits, leave it in play as long as you would have left the card it plays in play. Normally that will be the same turn's Clean-up. For a Band of Misfits playing a Duration card, it will be the Clean-up of the last turn the Duration card has any effects. For a Band of Misfits playing a Throne Room playing a Duration card, it will be the Clean-up of the turn the Duration card leaves play. For a Band of Misfits playing a card that can move itself from play, like Mining Village, the Mining Village can't move itself, so Band of Misfits doesn't leave play any earlier than normal. If a Band of Misfits plays multiple Duration cards (e.g., you used Throne Room on it), leave it out until the Clean-up of the last turn that one of them still had effects.
I think this rule is not consistent. It says to leave the BoM as long as you
would have left the card in play (if it had entered play). This is accurate for Durations, and for TR playing Durations. But it's not accurate for Mining Village. If Mining Village had entered play, you actually
would have trashed it. So then there seems to be an exception to the rule for cards that would have moved from play during the Action phase(?), which is hardly the intention.
So the rule has to be specifically for playing a Duration:
If BoM plays a Duration, leave BoM as long as the Duration would have stayed in play. From this it doesn't follow that BoM+TR+Duration makes BoM stay. If you want that, you need an additional rule:
If BoM plays a TR playing a Duration, leave BoM as long as the Duration stays in play.Alternatively it can be a Duration-like rule specifically about Clean-up:
BoM stays in play instead of being discarded in Clean-up if it played a card that would have stayed in play at that point. This covers both BoM+Duration and BoM+TR+Duration.