They could become a bicycle gang in Lumiose hanging out in dark alleys avoiding officer Jenny smuggling rare candies into Kalos. Ash could have a Jersey accent and have an entire harem but Serena would be okay with it and happy that she is his #1 girl. That is, until Serena gets pregnant, and he dumps her. Serena tries to take care of their kid but struggles as a single parent, and she and Ash are on and off all the time. She goes to her mom in desperation and Grace is like "I told you this would happen!!! I told you!!!!!". Soon afterwards, Serena sues Ash for child support but Ash claims that its not his child so they go on Maury and they sit uncomfortably while they await the results, which are "Ash, you are the father!". Delia comes up and smacks him and threatens to disown him if he doesn't marry Serena. Ash obliges and Serena is very happy and they live happily ever after.
:O Well maybe if Pokemon had an TV-MA rating xD
Yeah pretty much the "player" version of Ash here would be a Gary or an Paul lol. I still don't see how Serena would actually like this form of Ash rather than him being kind. I feel like his personality would be a deal-breaker for Serena.