From the Super Mario Wiki
The Toadley Clinic is a hospital owned by Dr. Toadley during the events of Mario & Luigi: Bowser's Inside Story and Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey. There are only two rooms in the area, one containing several Toads who have gotten the blorbs and Dr. Toadley's intern at the receptionist's desk, and one with Dr. Toadley in it.
Mario and Luigi go to the clinic the first time to check if Toadley knew how to stop the Dark Star, but the intern will not let them both talk to Toadley at the same time, so they fake the blorbs to get in together. Here, Toadley speaks of a disease called "Bowseritis" and points to Bowser as he enters the room. Here, Mario and Luigi fight the newly powered Bowser, defeating him. Toadley then tells the two of the Star Sages that hold the Star Cures, Wisdurm and Kuzzle. After that, Mario and Luigi do not return for a while.
The second time the bros come here is when Dr. Toadley speaks of the third Star Sage, Chakron, who lives on a mountain in Plack Beach. Before they go there, Dr. Toadley tests Mario and Luigi's air level to see if they are fit for the mountain's high altitudes. During this test, the clinic's ventilation system breaks due to Luigi's hard breathing, which malfunctions the breath-testing machine. This causes Birdley to freak out, flying around the clinic with the hospital's keys so Mario and Luigi cannot leave. After using the newly-learned Balloon Mario and Balloon Jump abilities to catch Birdley, Mario and Luigi head out to Plack Beach.
After gaining all three Star Cures, Mario and Luigi return to the clinic for a third time so Dr. Toadley can create the Miracle Cure, which flies around curing all blorbed Toads. The cure is then given to the bros so they can destroy the Dark Star barriers that block the entrance to Peach's Castle. Before the brothers head out to do that, the two are given all ten Toadley Clinic Attack Pieces from Dr. Toadley's intern, granting them the Mighty Meteor Special Attack.
Most of the Toads who were cured from the blorbs will leave the clinic, though some will remain there for the rest of the game.
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