The last episode of the original series was, "Hoenn Alone" which was the episode where Ash goes on a boat from Pallet Town to Hoenn. In this episode Ash is by himself, since Misty and Brock left in the previous episode.
This episode really consists of nothing more than Ash running around the port of the town as Pikachu gets separated from the group. The filler plot of this episode is a bunch of wild Haunter are harassing some random Rattata, Pidgey and Oddish in an alley. The rest of the episode follows standard filler plot fair with Ash battling TR and then going back to the boat to Hoenn.
My question is, why did the writers end the first series of Pokemon with such a terrible filler episode? They could have spent either an extra episode at Pallet or used the previous episode where Misty/Brock depart to be the "finale" of the original series. It was honestly as bad as most Johto fillers were, which isn't surprising since it was technically the last ep of the Johto arc too. Even when I was a kid I was wondering why they made such a lackluster transition episode from Johto to Hoenn.