mtg dual cards spell and land Mechanic Spotlight: Modal Double-Faced Double-faced card - MTG Wiki

This vampire knight turns all your sacrificed creatures into pressure and eventually more sacrifice fodder

It answers basically anything, and that flexibility is great

It is unlikely to ever be put on the auction block

Vivi Ornitier's effect is so good, and can be copied onto other creatures (something Izzet Cauldron decks do in Standard), so they too can provide mana to make for explosive turns where you can play your entire hand and draw a bunch of cards

You can use it to lock down your opponents' creatures, forcing him to walk into Wrath of God or other mass removal cards

If you want to use double sleeved cards, I'd recommend printing the v4 Deck Box , because it comes with a larger storage compartment