What happens if Mystic Reversal targets Moonfall with no units at the battlefield?
My opponent uses Moonfall and I Mystic Reversal it, but I have no units at the targeted battlefield. What happens when Moonfall resolves?

[Reaction] (Play any time, even before spells and abilities resolve.)
Gain control of a spell. You may make new choices for it.
Artist: Polar Engine Studio
Card Set: Origins
My opponent uses Moonfall and I Mystic Reversal it, but I have no units at the targeted battlefield. What happens when Moonfall resolves?
If I cast Discipline on Irelia Fervent at Abandoned Hall, do I get +5 total (2 from Discipline, 1 from targeting Irelia, 1 from Abandoned Hall, 1 from Abandoned Hall choosing Irelia)? If Defy counters Discipline, do the Abandoned Hall and Irelia bonuses remain? Does Abandoned Hall count as choosing Irelia if she is the only unit there?
If my opponent plays Time Warp and I respond with Mystical Reversal, what is the resulting turn order? Does the extra turn replace my normal turn or come in addition to it?