3 scenarios,

1. Ash Ketchum upon seeing Ho-Oh. It grants his wish to be the greatest pokemon master in the world by transferring him to earth. in the fall of 1981 in the woods near a cabin and he manages to activate the tape recorder contained therein.
2. Ash Ketchum upon defeating the elite 4 at the end of his journey manages to get translated into another world by Gary's final desperate attack. This is basically the same as the first scenario but Gary and his team are taken over by the deadites since they are weak when they come through.
3. Ash Williams manages to bind the deadites and read the banishing spell and everything in the cabin gets sucked into the vortex. Upon waking he is told by a woman he doesn't recognize that today is the day that he starts his pokemon adventure and he should go talk to professor oak. Though no one knows it yet the deadites have come to Joto.