tournament rules for double faced cards?

[billy92]

what are the tourney rules for 2 sided cards, how do you use them properly etc do you need a proxy?

[Jake1991]

You can either:

A. Use then in opaque sleeves and when the card transforms you take it out, flip it, and put it back in the sleeve.

or

B. Use a Checklist card to represent the card and have the Dual-Faced cards put aside until you need them.

Also, only official Checklist cards may be used to stand in for Double-Faced cards in a deck.