Ash learned from a mysterious man eith psychic powers he must obtain a ghost type pokemon. Ash travels to Lavender Town and finds pokemon tower. Walking by graves holding dead pokemon.
He runs the whole time. Until he dies, then he becomes freinds with Haunter and possesses himself. He then heads back. Being stopped by Team Rocket temporarily. They got scared off and ran away.
Ash ran into Sabrina's gym. "It's over Sabrina. I have a ghost type." Sabrina looks at Haunter "1 on 1?" "Yeah!" She sends Kadabra but Haunter doesn't attack instead he makes funny faces. Kadabra laughs so hard he can't battle. Sabrina laughs too, until she notices.
"The boss will probably fire me for this. For defeating me, I shall return your pokemon to you" she does so "You may take this as well" giving Ash a marsh badge. "If I can't work for him anymore. Maybe I should focus more on being a gym leader. If you want, that haunter is pretty funny. Mind trading for my Kadabra?" Ash thinks about it but decides to do it. After it happens Ash looks at Kadabra "Huh? It's...evolving?" Sabrina says "Haunter too" Both evolve "Trading causes some pokemon to evolve"
"Bye Sabrina" Ash leaves knowing a bit more about pokemon. Next stop is Celadon city, but what comes next for our hero. The only way to know is to keep reading, or watch the show. (A/N That trade only was there to show off trade Evolution. The show didn't do that until Unova)