Pokémon Mystery Dungeon: Unbreakable Bonds
JoshTheIcarusKid
Nothing is stranger than turning into a Pokémon. Ash would know because that just happened to him.
Ash wakes up on the shore and finds himself transformed into a Pokémon and transported into a new, strange world. Ash creates his own exploration team with friends both new and old, faces against new villains and rivals, and harnesses new power in order to protect his team and this world.
Eventual Amourshipping, Ash/Serena but not immediate.
Warning: Pokémon battle will have some injury and blood. Nothing too gory, but just a warning.
Cross-posted on ao3 account: HappyJester