Interesting, but I'd say it costs a little much.
Why would you say that? This card is quite strong because it has the ability to remove high quanta creatures from the field. This could be severally damaging to pillarless rush decks, high quanta creature decks, and pharaoh/firefly queen decks. These are the reason I justified the cost being 13/12.
Compare Reverse Time with Chaos Seed. Then Time Warp with Pandemonium. Time Warp should cost more than Pandemonium, but not THAT much.
EDIT: This is actually pretty dang strong, I don't know anymore. ^.^