um... i'm not going to continue posting on Ravecat's thread, but THAT'S THE POINT!!!
substitute lowers you're health, so the opponent almost kills you, then you pain split, healing you, and if substitute is still there (which it normally isn't) you will-o-wisp, you're meant to be slower!
trust me, i've tried it, it works, and if you don't believe me, go on shoddy now, i'll challenge you!