Grass Hysteria! (Japanese: 禁断の森の王者！フシギバナ！！ King of the Forbidden Forest! Bulbasaur!) is the 33rd episode of Pokémon: Advanced Challenge.
The gang is lost in a forest - even Max's PokéNav shows nothing. Brock's compass shows different directions, adding it to May's fear. A Skarmory begins to chase them. May's Skitty goes out and May protects it, but in so doing, Skarmory grabs her and sends her away. Ash, Brock and Max go after it, but find two men blocking the path. They explain that nobody is supposed to go on the other side of the gate. When Ash mentions that May's been carried there by a Skarmory, they go to speak with a man, so they follow.
May is seen to be carried on a peak. She takes Skitty back to a Poké Ball and sees a Bulbasaur. Bulbasaur gets a flower, but begins to fall down, so May catches it in time. Bulbasaur is a bit taken back, but befriends May when it tickles May using a vine. However, a Sunflora, Weepinbell and a Vileplume defend it. The old man is being told the problem, but cannot help Ash, Brock and Max, as the Grass Pokémon will be angry. Nevertheless, they will go to see how to deal with the situation. Team Rocket spies so they plan to steal those Grass Pokémon. Sunflora uses Razor Leaf, Vileplume Stun Spore and Weepinbell Vine Whip on May, defending the Bulbasaur.
Bulbasaur attempts to calm them down, but more Grass Pokémon arrive to attack May. To protect herself, she sends Torchic to use Ember. Torchic negates the attacks and goes with May. Bulbasaur goes as well, but is stopped by a Sunflora. As the men discuss, Ash, Brock and Max leave to go get May. The men notice Poochyena barking, so the men spots the gang left. Brock, Max and Ash tackle the gate, but they have to climb the vines to get across. The vines break, so Ash and Pikachu are the only ones to go get May back. May hides, but soon has to go out due to Stun Spore. The next thing she knew, she is surrounded by the Grass Pokémon. However, Ash arrives to the scene.
Pikachu uses Thunderbolt, clearing a path for them to escape. They go (with Ash explaining that the land they are on is not for humans). Pikachu uses Thunderbolt for Ash and May to pass. While their path is blocked, Torchic calls them to go near him. Soon, they stand on an edge of a cliff. The Grass Pokémon attack, but are stopped when a Venusaur comes. Venusaur checks Ash, May and Torchic - Bulbasaur that came to May seems to have warned him that they are not for any fighting. Ash and May are taken to a waterfall. Bulbasaur gives May the flower, reminding Ash of his own. Bulbasaur grabs May with a vine, going off, so Ash goes with her.
They see the forest they have been lost in before. May sees a town and explains the Bulbasaur what it is. The old man explains to Max and Brock that the Grass Pokémon were hunted by men, so they became enraged. To prevent any damage, some people built the gate for protection. The land has some magnetic field, preventing some machines to work. Team Rocket begins to steal the Grass Pokémon. Pikachu uses Thunderbolt, but the attack is deflected due to the mirror. The men, Brock and Max hear the Bulbasaur being taken.
Venusaur attacks them. Team Rocket goes to take it, but Venusaur uses Vine Whip and goes to take the Grass Pokémon. Meowth switches to go forwards, making Venusaur harder to take the Pokémon back. Meowth switches to backwards, so Venusaur is knocked out. Bulbasaur is taken, so May comes as well with it. Just as the Mecha was about to grab Venusaur, the Pokémon tackle the robot's bag. Bulbasaur uses Razor Leaf, freeing all the Pokémon from the robot. But, just as the robot is about to recapture the Pokémon, Obee's Poochyena use Shadow Ball, blowing the hand to pieces.
Pikachu uses Thunder, but the attack is also deflected. However, Venusaur uses Solar Beam, blasting Team Rocket away, as the Robot wasn't able to counter it. Everyone apologizes to the Grass Pokémon for disturbance and May says goodbye to Bulbasaur. However, Bulbasaur (after some thinking) goes to May, joining her.
- Featured Pokémon: Manectric, Electrike, Mantine, Electrode.
- In the beginning of the episode, a classic Pokémon identification can be seen. In this case, it is a Charmander.
- The title is based on the phrase 'Mass hysteria'.
- This episode is featured on the Volume 1: Grass copy of Pokémon Elements.