Stu & Pid are obstacles in SMG3's lair to prevent Mario and SMG4 from stopping him from uploading a video containing content of SMG4's weirdest and most embarrassing moments. They debut in SM64 Bloopers: SMG3's Gauntlet of Gloom.
Stu and Pid are Piranha Plants who seem to be brothers, and as their combined name suggests, they are StuPid. They constantly fight over small things and call each other dumb which is, in fact, true, again relating to their combined name.
Stu is a yellow Piranha Plant with white polka-dots and is Pid's brother, Stu is the plant who is a liar and according to him, Pid likes to show off with saying stuff to make him "look tough".
Pid is a purple Piranha Plant with white polka-dots and is Stu's brother. Pid tells the truth. He apparently annoys his brother to the point that Stu says that the stuff he does is dumb.
Mario and SMG4 enter a mysterious room with two doors leading to a room. Mario is about to approach a door when the two plants rise from the ground with Pid demanding the duo to "stop right there". Pid threatens the pair by saying to Stu that they have "fresh meat". Stu then accuses Pid of trying to "look tough" which Pid naturally denies that is true. Then it causes an argument that distracts them for a moment. Mario attempts to run for a door but he is blocked just in time by Stu. Pid and Stu then urged Mario and SMG4 to solve their riddle, Pid then does an evil laugh which causes Stu to say that they already agreed on no evil laughing which yet again causes another argument. Stu saying that evil laughing is "dumb" while Pid says that Stu is "dumb".
The plants tell Mario and SMG4 that one door leads to another room while another leads to their "ultimate doom". Pid then asks Stu if he can do an evil laugh again, which Stu replies with a sigh and then finally grants him permission only to do it "just this once". SMG4 then approaches Stu to ask what would Pid say about the door that leads to the room. Stu says that Pid would say it is the door on the right that would lead them to the safe room. However, SMG4 knows that it was the left door that would always lead you to the safe room since Stu is the liar.
Mario does not understand how this works, so SMG4 attempts to explain the way Mario understands by using spaghetti, being Mario's favorite food. Mario still does not understand so SMG4 takes Mario with him into the left door that is safe. Pid then says "those guys were pretty nice" but Stu says he is unsure about Mario being the "retarded one" and says that he reminds him of Pid, in which Pid replies about Stu "wanting to have a go at him" causing the final argument until Bowser shows up. They then greet Bowser by calling him a "giant turtle" and tell him that he must solve their riddle. Bowser decides that he cannot be bothered doing so and burns the plants with his fire breath before heading to the right door.
Stu and Pid are two of the many Piranha Plants that Peach set on fire in the garden. However, they are enjoying it.