Doctor Sigmund Shrinkasaurus

Doctor Sigmund Shrinkasaurus is a self-proclaimed nose, foot, elbow, and brain specialist in Brain Drain. He is a goose who speaks in an indecipherable accent. His office is on Dinosaur Land, at the opposite side of Dinosaur Lake. Sigmund Shrinkasaurus gets his name from the popular neurologist, founder of psychoanalysis, while his last name comes from "shrink," a slang term for a therapist.

Depending on the reader's choices, either Luigi by himself (in the body of Princess Toadstool) or Luigi and Toadstool (in the body of Mario) can arrive at Doctor Sigmund Shrinkasaurus's office. They decide that Sigmund may help with the rampant mind-swapping and enter his office. Regardless of who arrives, Sigmund is left frustrated by what he thinks to be people talking nonsense, but he lets them settle onto the various couches around the office. The group then tells him that the mind-swapping happens after a radio is turned on, leading him to turn on a nearby radio. Luigi's mind is then switched with that of a Koopa Troopa in the Koopa Command Center. Later, as Mario and Luigi (still in the Koopa Troopa's body) attack the Koopa Command Center, Sigmund, Toad (in Toadstool's body), and Toadstool (in Luigi's body) fly in on a large floating couch. He lands next to the two of them and lets everyone regroup. Mario insists on chasing Iggy Koopa to WMUSH, but Toadstool says that Sigmund can bring everyone back to their original body, leaving Luigi to decide if he should follow Mario or stay with Toadstool.

What follows is a puzzle where the player is given an image of Sigmund at his desk and then a set of instructions that all good nose, foot, elbow, and brain doctors must follow: All of them must have at least two pipes on their desk (which he follows), never have more than three teddy bears in their office (which he follows), and have more teddy bears than pipes (which he does not follow, as he has three teddy bears but four pipes). If Luigi still decides to stay with Sigmund, Sigmund tells him to lie down as he counts backwards from ten. However, when he reaches one, he exclaims, "Oops!" and Luigi finds himself in the mind of a parrot in a pet shop, leading to a Game Over.