Valki, God of Lies

You don't choose which creature card exiled with Valki that Valki will become a copy of until that ability is resolving. (In many cases, the value you chose for X will give away your intentions.)

In the Commander variant, a double-faced card's color identity is determined by the mana costs and mana symbols in the rules text of both faces combined. If either face has a color indicator or basic land type, those are also considered.

If an effect allows you to play a specific modal double-faced card, you may cast it as a spell or play it as a land, as determined by which face you choose to play. If an effect allows you to cast (rather than "play") a specific modal double-faced card, you can't play it as a land.