After arriving in Nacrene City and discovering that the Nacrene Gym is inside the city museum, our heroes meet a very scared man. His name is Hawes, and it turns out that he’s soon to become co-curator of the museum. He claims to have seen ghostlike apparitions recently, just as the museum is about to launch what is called the Secret Artifact Exhibition. The gang listens to the details of what has been happening, and Iris decides that an “angry spirit” is putting a curse on the museum. Cilan disagrees — he says that there must be a scientific explanation for everything.
While spending the night at the museum to investigate, our heroes and Hawes discover that a Yamask mask, which Hawes had mistakenly thought was a replica, was actually a real Pokémon! It was this Yamask that was appearing to haunt the museum, when really all it was trying to do was get its mask back! The Yamask was after Hawes for unwittingly taking the mask away, but the Pokémon forgives him and happily exits with its mask.
Then Hawes’ wife Lenora shows up. She’s the Nacrene City Gym Leader; Ash challenges Lenora to a Gym Battle, and she accepts! So now Ash’s second Unova region Gym Battle begins—hopefully it will lead to his second Unova Gym Badge!
Ash goes to the Battle Gym (which is a museum). However, Cilan, Iris and Ash spot a sign that the museum is closed. A man screams and manages to go outside. The man addresses himself as Hawes and is the proprietor of the museum.
Hawes tells that when the new collection of relics were moving in, odd and dangerous things happened, like a strage glow was chasing him. After days, he closed the museum, but was chased (again) by the purple light and finally went outside.
Ash, Iris and Cilan promise to discover the truth of it - either using Cilan's science or Iris's ghost powers. They look around the exhibition and sleep for the night in the museum. Meanwhile, Team Rocket and the mysterious man make their next appointment.
Ash, Cilan, Iris and Hawes were awoken. The room is filled with a dark fog, while an armor is walking. Pickachu defeats the walking armor, but the armor somehow reassembles itself. Oshawott comes out of his ball and attacks it, defeating the armor.
In the room it starts raining, Iris, Cilan, Hawes and Ash go to a dry place in the museum. The crew sees a mask moving behind the safety glass. Hawes explains that he thought it was a replica of Yamask's mask. Nearby, a replica of Dragonite's skeleton is moving!
Suddenly, a woman declares an attack from Watchdog, attacking the replica with a shining light! The skeleton disassembles, revealing a Yamask. Lenora, the woman who owns the Watchdog, explains that the mask was Yamask's, but the Pokémon lost it because he was sleeping and Hawes thought it was a replica, then Yamask had to go through the ghost routine to get his mask back.
Hawes gives the mask back and Yamask goes away from the museum, with Ash, Cilan, Lenora and Hawes wawing that Yamask. In the end, Ash decides to battle Lenora.
- The Moveset the Yamask used in this episode is as follows:
- Psychic to move the armor and skeleton of a Dragonite.
- Haze to create a fog.
- Rain Dance to cause indoor rain.
- Will-O-Wisp for a spooky flame.
- The title of the episode is a parody to the movie "Night at the Museum"
- This is the last episode so far Pikachu used Volt Tackle.
- Professor Oak's Live Caster: Axew
- Who's That Pokémon?: Yamask (US)