Drowzee is first met in Treasure Town, where he is helping Azurill and Marill to find a lost item.
However, he is later revealed to have kidnapped Azurill so he could access a treasure supposedly hidden inside of a small cavern at the peak of Mt. Bristle. He was confronted by the player and partner shortly after and fought them. After he is defeated, he is arrested by Magnezone and the Magnemite.
A long while later, when Azurill has nightmares, it is revealed that he was let out of prison for good behavior. Having expressed remorse for his actions, he holes himself up on Mt. Travail for training and to learn self-discipline, and it is also revealed that he has the power to get inside the dreams of others. He is asked by the player and partner to help Azurill. He accepts because he is sorry for what he did to Azurill before and wants to make it up to him. He then sends the player and partner into Azurill's nightmare, telling them that if he went along they would only be slowed down.
Afterwards, he becomes good friends with Marill and Azurill, but leaves Treasure Town to begin travelling soon after the player and partner defeat Darkrai.