The Ancient Puzzle of Pokémopolis (げきとつ！ちょうこだいポケモン A Battle of Ancient Pokémon) is the 74th episode of Pokémon: Indigo League.
After an accident, the heroes discover some ruins. Team Rocket goes inside and find a relic, but this causes a giant Gengar to appear, which absorbs everything. A relic the heroes found at the ruins summons an Alakazam, who fights Gengar, but the legend says that these forces will destroy everything. To soothe them, Jigglypuff sings a song, but this has no effect, except that a third giant is summoned to solve the conflict...
Ash and Brock have the battle: Pikachu and Vulpix use Agility. As Vulpix goes to use Flamethrower and Pikachu use Thundershock. However, Jigglypuff appears, so Pikachu and Vulpix redirect their attack on a cliff, crashing it. The blast caused the heroes to uncover a building, a temple of sorts. Brock uncovers an artifact, which a girl takes and presents it to her professor. Brock tells them he found the artifact, though the girl ignores him, Ash and Misty, as they want to uncover the artifact. Team Rocket sees the temple as well and think about their next plan.
The heroes see a statue to Psyduck and Misty remembers the city was named Pokémopolis, leading Brock to believe that the city is near them. Professor rushes to doctor Eve (the archaeologist) and gives her the spoon, which looks similar to the former object. Ash and Misty are surprised to hear she is a doctor, even if she is young. The professor states she was always interested in Pokémopolis and graduated with very high grades. As Eve pushes the professor out, the artifact resonates to the spoon, with Pikachu feeling this presence.
Eve shows a tablet in which states when the night comes, the two destructive forces will destroy anything in their path and no human will know how to stop them. Eve admits it is a hard mystery, so Brock goes to uncover it, making Eve think he likes mysteries, but Ash and Misty know it is something else. Meowth thinks Jessie and James should bow to him, but gets punished by this statement. As the heroes sleep, the artifact resonates and the spoon begins to move. Team Rocket goes to the temple and Jessie sends Arbok to search for the relics inside it. Jessie asks what will James do with the treasure. James replies he will pay the boss what he owes to him, making Jessie mad for such a statement. James corrects himself and thinks he can be the boss instead.
Arbok came with some strange relics. Though Team Rocket are disappointed, Arbok gets absorbed into the relics, while the artifact and the spoon resonate. The relics begin to make stomping noise. Team Rocket goes to escape, but get stopped by a force. Next day, the heroes and the archaeologists see the relic. The professor picks it up and gets absorbed. Everyone runs away, but the relic stops some archaeologists and absorbs them. The heroes go into a cabin and soon see everything floats around. The relic forms itself into a giant Gengar with strange markings. Eve sees this dark device is mentioned on the tablet. From a distance, Oak mistakes that a storm is approaching. Ash, Misty and Brock go to stop this Gengar from going to Pallet Town, while Eve goes to study the mystery.
Brock sends Onix, who digs to stop Gengar. Ash sends Pidgeotto, who uses Gust, but gets absorbed by Gengar, into the place where the other archaeologists and Team Rocket are. Brock's Onix binds Gengar, but gets absorbed as well. The heroes go to the cabin and see Eve under a spell, floating. The spoon unlocks the artifact and goes out, forming a huge Alakazam with some markings. The Alakazam and Gengar fight, while Eve understands they have destroyed Pokémopolis and now they are going to destroy everything around them. Ash goes to capture them, as he tosses the Poké Balls. The Balls are destroyed, while Gengar and Alakazam stop the heroes and Eve. Pikachu goes into water and electrocutes Gengar and Alakazam.
The Gengar and Alakazam continue their battle. Jigglypuff rolls to the heroes, so they believe it could put them to sleep. The Jigglypuff sings, but there is no effect on the giant Pokémon and gets blasted off. However, this caused a third object to awaken its powers, as a big Jigglypuff emerges. The Jigglypuff sings and stops the fight, as everyone goes to sleep. The Jigglypuff sees Gengar and Alakazam asleep and uses the object as a brush to paint on their faces. Eve wakes up everyone. Team Rocket is glad they survived, but seeing the twerps, they run away. Brock thinks Jigglypuff saved the Pokémopolis, leading Eve to believe these stuff were the first Poké Balls. With this, Eve knows this is a secret she must uncover.
- 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.
- In Canada Version, "To Be Continued" graphic is replaced by "Stay Tuned".
- When Ash asks about the Pokémopolis, his shirt was discolored.
- Although Arbok was the first Pokémon to go into the Dark Device it is never seen for the rest of the episode.
- In the Japanese version, Brock tells Vulpix to use Quick Attack. In the English dub, Brock tells Vulpix to use Agility, a move it can't learn in the games.