Hm. Mostly useful on your own Elbrus, the Binding Blade or Ludevic's Test Subject. Will do mad, mad things in-set, and should perhaps cost more for this reason. I'm reminded of how Fold Into Aether cost way more than the then-standard Counterspell despite being worse on opponents' spells.

Might want the reminder text from Interception.

Or in fact, I'm not completely convinced this works at all. Is the idea that when the light side here starts resolving, it processes the text from the light side, does it, and then if that transformed this spell, it then processes the text from the dark side? I'm not sure that works.

Anything works with a Comprehensive Rules amendment. :3

The back side needs to say "Counter target spell that targets a double-faced object."

I don't think that's a good idea. Assuming the idea is that during the resolution of Reversal of Fate, it might transform into Falsify and then evaluate Falsify's text: then Falsify would never be checked for legality of targets, and it might well resolve even though its target doesn't meet its current targeting condition.