Apparently he does nothing in the latest one, despite Mewtwo and Genesect Red falling through Earth's atmosphere, it seems like they only added him to the Decola (?) Islands arc in an attempt to lure in older fans, with misleading episode previews that shows Butterfree coming back? nope, it was a different one...he was just thinking of his as a random Caterpie evolved.
They never said Butterfree was going to return. They said that Ash meets a Caterpie has remembers his Butterfree, and then people ran with this.
"Murder of the living is tragic, but murder of the idea is unforgivable." - Janus, speaker of the synod