Ash's Pikipewpew is a one of a kind Gun/Flying type Pokemon. It was first captured on Episode 7: Grand Theft Pikipek as a Pikipek and was then used as a weapon. It was not seen again until Episode 40: Return of the Summaries, where it immediately evolved into Pikipewpew. Since then it has gone back and forth between life and death, and is the first non-fully evolved Pokemon to successfully fuse with Ash.
It evolved into Pikigatling on Episode 163, yet soon reverted to it's previous form for unknown reasons. It once again evolved into a Pikigatling on Episode 223: I don't even, except it's evolution was maintained. In Episode 225: Dave Vs. Ned it showed that it is still able to merge with Ash. Ash-Pikigatling was able to KO Dale after he had shot Hank Hill.