Books tend to offer card advantage, so card draw, discard, and hand size will be recurring themes, but we could see lots of others
Protect your collection from the scammers
Being an enchantment would normally be a downside on a creature this expensive since it dies to enchantment removal as well, but it has hexproof anyways so that matters a lot less
There's plenty of utility in between those extremes
Imprisoned in the Moon is not a card that you build an entire deck around, but it is a flexible role player that gives blue the ability to nullify cards that it normally doesn't interact well withlands and planeswalkers
Again, Doubling Seasons effect will create twice that many tokens, so you will be getting 4 Jace, Cunning Castaway tokens, each entering the battlefield with 6 starting loyalty, same as the original