Aatrox, The Final Darkin

First strike, flying, lifelink.
Whenever Aatrox, The Final Darkin dies, you may pay {x}{x}, if you do, Exile it with 15 minus X time counters on it, when you remove the last time counter, return Aatrox into play under it's owner's control, with haste, and must attack that turn, if possible. (You may not pay 0 for X.)
"Pain is temporary, victory is forever!"