[This disappeared off the internet for various reasons. It’s all still correct (with one exception that I’ve noted below), so I figure it’s worth giving a home somewhere.]
They’re here! Hopefully by now everyone is aware that Innistrad contains double-faced cards. These cards have another card where there would normally be a traditional Magic back, and there obviously need to be new rules to handle these. Here are some of the questions that have come up most often.

In general, things shouldn’t be too complicated. Knowing a couple of rules and applying a little common sense should hopefully get you to the right answer.

How do players use these cards in game play?

Because the cards have two sides, a few changes have to be made to deck construction and play rules. At the heart, players have two options – they can play with opaque sleeves or they can play with checklist cards. If they are playing with opaque sleeves, everything works just like usual. If they are playing with checklists, then a few new rules come into play and it should work out just fine. Don’t panic.

What’s an opaque sleeve?

Opaque means that no matter how long you stare at the back, you won’t be able to tell what’s in there. Be careful! A lot of colored sleeves aren’t actually opaque – you can sometimes make out the Magic logo and the white dot.

What if someone tries to use some of these not-fully-opaque sleeves?

Not using fully opaque sleeves in this situation should be treated as Marked Cards. If the difference can be seen through the sleeves in normal game-play (as opposed to carefully angled under a light source) this is a strong candidate for the appropriate upgrade.

OK, so checklists. Aren’t these just proxies? Can I just sharpie up a plains?

They are not a proxy. They have their own section in the MTR.

As a special exception at the Prerelease *and at no other time* judges have the option to issue a checklist proxy if the following conditions are met:

• The player is unwilling to purchase opaque sleeves
• The player or judge is unable to procure a checklist card from anyone else in the venue.

At all other times, only the official checklist can be used to represent a double-faced card in a deck.

Are there rules for how the checklist needs to be filled out?

Yes. A single item should be obviously and unambiguously marked. A card without a mark, or multiple potential marks should be treated as an illegal card.

How will I get hold of enough checklist cards?

Odds are you’ll be awash in them. They come in 7 out of every 10 Innistrad booster packs. You also get 10 checklist cards when you buy an Innistrad Fat pack. That’s… a lot of checklist cards. Ask your store guy if they swept up any into the token box. [2016 note: no idea if this is still true for Shadows over Innistrad, but there’s a lot of them.]

What about altering them?

Sure! Follow the usual rules for altering – it can’t be marked, and has to unquestionably be the checklist card underneath. I would say that trying to move the name of the card is probably a bad idea, but getting rid of everything but one name can be treated as unambiguously marking the card.

Will there be foil checklist cards?

No.

So how will it work if you’re using a checklist?

If you use a checklist in your deck, then every single double-faced card you own is treated the same way as we treat tokens. They don’t exist when determining deck legality and don’t exist if you accidentally shuffle one into your deck. Make sure you don’t use a mix of double-faced cards and checklists, because then you’re likely to end up with an illegal deck. [NOTE: This is no longer true. For each different double-faced card, you need to be consistent, but you can have all of one double-faced card in your deck and all of another one represented by checklists.] I recommend announcing this to players before the tournament begins to avoid problems.

Do they exist during deckchecks?

They sure do! You need to present the double-faced cards to your friendly deckchecking judge so that they can verify that you have the cards you’ve written on the checklist with you. A checklist without a corresponding ‘real’ double-faced card is an illegal card. Having more double-faced cards than checklists is OK (see the next question), but if they’re cards that don’t correspond to something in your deck, it’s likely to raise awkward questions.

Can I have ‘night’ versions of the card that I switch in and out when they transform?

As long as they are additional copies of the card, then yes. If you are playing with checklists, then it’s no problem, as you’ll simply be swapping back and forth between ‘day’ and ‘night’ versions. If you are not using checklists, it’s still fine, but make sure that if you keep them with your sideboard they are in a different colored sleeve that makes it obvious that they are there solely to be ‘night versions’. This is an exception to the no-cards-with-sideboard rules.

If I am using checklists, can I look at the actual double-face cards at any time?

You can. You are allowed to look at double-faced cards you may have on you at any time. This is an exception to the usual “no Oracle text” rule, and only applies to the cards themselves.

Do I have to reveal to my opponents which double-faced cards I’m playing?

No. You may be keeping the cards with your sideboard, but they are not actually part of your sideboard and don’t need to be presented. If you have unfortunately been Mindslavered, the cards don’t exist somewhere that they can look at them. Well, except for the ones that they can see the checklist card for.

How do the checklist cards work with Cabal Therapy?

Naming ‘checklist’ is illegal and will get you frowned at. However, just as with flip cards, naming the night side of a double-faced card is sufficient for uniquely identifying the card.

Note that this is not true for cards such as Runed Halo and Pithing Needle. You need to name one side or the other as they only affect that side.

OK, that all sounds like it should work. But drafting?

Drafting works mostly like it always has, but with a couple twists. Essentially, some cards in the pack convey information that is traditionally hidden from players in draft. That’s not a mechanical problem, it’s just… different. You’ll have to factor in how much information you’re giving away as part of evaluating which card to pick. Since there’s a double-faced card in every pack, each of the other players drafting will be making the same decision.

Can I hide what I’m picking?

No. This is a change from what was originally announced. Your pick goes on top of your pile, and if you pick a double-faced card, you can put it on top with either side face up (the rest of your cards still need to be picked face-down!) After the review period between packs, you can leave whatever card you want on top.

I’m really curious which double-sided cards the people around me opened. Can I look?

That would be bad. There is a whole lot of other information you are not allowed to see, and there’s not much of a line between finding out what double-faced card a person has in their pack and what other cards they have.

One acceptable practice is to have all the players open their packs and reveal their double-faced card to everyone for a brief review period before drafting the pack. This is not required, but you may find it cuts down on later jockeying.

Can I ask?

While the cards are information that it is not illegal to reveal during draft, you are not allowed to go to great lengths to find it out, which includes (strategic) talking during the draft.

I’d really like to know if the person feeding me is taking a double-faced card, but he’s refusing to pick until I do. Help!

In a Competitive or Professional event, with a timed draft, this is not going to be a problem. In a Regular event, if two players are deadlocked in making a pick, then the player who is closest to feeding the other player that pack must pick first. If the players are equidistant (such as in seats 1 and 5), then the player in the lower-numbered seat makes the pick first.