Westvale Abbey, even moreso than other double-faced cards, has two completely different sets of characteristics for its front and back faces. This matters when it comes to Commander, as only the front face of a card counts when determining what can go into the commander slot. Since Westvale Abbey is a land, which is neither legendary nor a creature, neither Westvale Abbey nor Ormendahl, Profane Prince can be your commander (not that you’d be able to cast Ormendahl from the command zone anyway).
What about inclusion in the 99 cards of any other commander deck? Well, here the back face does matter. The color indicator dot on Ormendahl (in the type line, to the left of the types) indicates that it’s a black card, which means it can only go into decks whose color identity includes black. Note that the Westvale Abbey face, itself, does not have a color. Lands are by default colorless, it only produces colorless mana, and although Westvale Abbey can make creature tokens that are both white and black, color words in the text of cards don’t count — only colored mana symbols and color indicators. Combining the two faces gives the card, overall, a Commander color identity of just black.
Today’s Rules Tip written by Jen Wong