Ash is training against Brock. Pikachu is battling Vulpix until Jigglypuff gets in the line of fire. To keep Jigglypuff from getting hurt, Pikachu holds back its attack and Vulpix deflects it’s fire attack to uncover some ancient artifacts. A girl named Eve swoops in to take the artifact they found. She explains about the ancient city of Pokémonpolis and tells of a warning written on an old tablet but she cannot understand it. In the night, Team Rocket sneak in to steal any valuable artifacts they can get out of the unsearched underground. Arbok, who was sent in to find them, comes out with a small black bar-like object which traps him inside along with the rest of Team Rocket. The group come out the following morning to discover the object on the ground. It captures the leader and some workers but the rest make it safely back to their camp to see the black thing turn into a giant Gengar. They then notice everything floating around inside. Ash, Misty and Brock go to stop the Gengar from destroying Pallet Town, but get its attention along with some of their Pokémon forcing them to retreat back to camp. They discover Eve under the spell making everything float. The glass around the artifact breaks, and the key to it connects. Then it turns into a giant Alakazam. The two giant Pokémon battle it out, until Jigglypuff sings a song, that doesn’t work on them. Jigglypuff is flung off into the air, but it’s song makes another artifact turn into a giant Jigglypuff. it starts to sing. Then, that puts the giant Pokémon to sleep and it whips out a paint brush to paint designs on their faces. The giant Pokemon are then gone and Team Rocket and the others are freed.
Like Jigglypuff's microphone/marker, the relic which unleashed the giant Jigglypuff was also a microphone that doubles as a marker.
The giant Jigglypuff's song was deeper than the normal Jigglypuff song.
The "Who's that Pokémon?" in this episode is Jigglypuff.