Leinore helps guarantee you almost always hit your coven trigger by putting a +1/+1 counter on any creature you control, then, if you control three or more creatures with different powers, you draw a card
This versatile tutor can summon up anything you need, from a Badgermole Cub for extra ramp, to a Reclamation Sage to handle a tricky permanent, to Craterhoof Behemoth when it's time to win the game
Miracle spells only get better as Wizards keeps printing new ways to manipulate the top of library, the most recent addition being Mystic Sanctuary
Preordain If this was a Modern or Legacy-only list Id probably bump Preordain even higher, but its only slightly better than Serum Visions in Commander
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
You must play the cards as you resolve the last ability