It doesn't have a once/turn thing
Extra cards included to test new strategies
Decks that want to draw cards with Fact or Fiction are very unlikely to also be able to optimally use a Skullclamp, decks that have the mana to bust out a five or more mana draw spell are similarly unlikely to also want to use the economic but slow Ancestral Visions
Omnath, Locus of Creation is one of the strongest landfall cards, to the point many decks have been built around it and it was deemed too powerful in several formats
Aside from flavor, you can interfere with opponents who are using typal effects like Distant Melody or Coat of Arms for value by changing their creatures to other things
Okay, Big Shot gives all of your characters with the Bodyguard keyword a boost of Resist plus one and also allows them to quest for an additional lore, but only when Little John, Resourceful Outlaw is exerted