Just to confirm: when a card cares about the greatest mana value of a commander(s) you own in the command zone (such as Visions of Ruin), if your commander is a DFC (like Valki, God of Lies), Visions will reduce its flashback cost by 2 rather than by 7 because Tibalt, Cosmic Impostor’s side isn’t counted.
For purposes of Visions of Ruin, a double-faced card (modal or otherwise) in the command zone has only the front face's characteristics (C.R. 712.4a).
Remember that in general, you can choose between a modal double-faced card's front or back face only at the moment you're playing or casting that card (C.R. 712.7, 712.8), and not when you're moving it from one zone to another for any other reason.
Note that if you cast Visions of Ruin with flashback, its cost reduction can reduce its cost by more than 8 if it would otherwise have more than eight generic mana in its cost (e.g., due to Thalia, Guardian of Thraben) (C.R. 601.2f). This cost reduction doesn't reduce the "flashback cost" (which is 8RR) (C.R. 702.1a), but rather the cost of the spell. Compare Visions of Ruin with Henzie "Toolbox" Torre; see also:
Is this correct?
Remember that in general, you can choose between a modal double-faced card's front or back face only at the moment you're playing or casting that card (C.R. 712.7, 712.8), and not when you're moving it from one zone to another for any other reason.
Note that if you cast Visions of Ruin with flashback, its cost reduction can reduce its cost by more than 8 if it would otherwise have more than eight generic mana in its cost (e.g., due to Thalia, Guardian of Thraben) (C.R. 601.2f). This cost reduction doesn't reduce the "flashback cost" (which is 8RR) (C.R. 702.1a), but rather the cost of the spell. Compare Visions of Ruin with Henzie "Toolbox" Torre; see also: