Valki, God of Lies // Tibalt, Cosmic Impostor

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.

A modal double-faced card can't be transformed or be put onto the battlefield transformed. Ignore any instruction to transform a modal double-faced card or to put one onto the battlefield transformed.

You can activate Valki's ability multiple times in response to one another. This may briefly allow Valki to copy different creature cards. You'll get priority to cast spells or activate abilities in between each of Valki's activated abilities.

The mana value of a modal double-faced card is based on the characteristics of the face that's being considered. On the stack and battlefield, consider whichever face is up. In all other zones, consider only the front face. This is different than how the mana value of a transforming double-faced card is determined.

The emblem given to you by Tibalt allows you to play cards exiled with that specific Tibalt, Cosmic Impostor, even after that Tibalt leaves the battlefield. If a different Tibalt, Cosmic Impostor comes under your control, it's a new object (even if it's represented by the same card). Of course, the new Tibalt will also give you an emblem so you can play the cards he exiles.

If an effect begins to apply to Valki before it becomes a copy, that effect will continue to apply.