Gigantic, Glow-In-The-Dark, Robo-Squid

The Gigantic, Glow-In-The-Dark, Time-Traveling Robo-Squid (Supa-Squid), is a giant robotic squid built by Melvin Sneedly. It is superior to its predecessor, the Purple Potty, as it does not require a day to cool off in between uses.

Captain Underpants and the Tyrannical Retaliation of the Turbo Toilet 2000
The Robo-Squid suit was built by Melvin Sneedly in the year George and Harold were absent due to being mistakenly arrested by police (who believed that they had robbed a bank, which in fact was done by their alternate selves). Due to Tippy's time travel, this timeline was erased and replaced by one where George and Harold disappeared on a time-traveling escapade, however, the duo was still absent indefinitely in this timeline. This initially pleased Melvin, as he now had peace and quiet to conduct his experiments, however, when the Turbo-Toilet 2000 was freed from Uranus and returned to Earth, he used his Robo-Squid suit to rescue Captain Underpants so he could defeat it (Melvin initially tried becoming a super-hero himself, but found he disliked it due to peoples' abuse of the system). George and Harold later borrowed the Robo-Squid suit after they found their teachers had scheduled important tests for them on the day they were absent (due to sleeping in because of their exhaustion from their previous escapade). This created additional versions of themselves and the Robo-Squid suit (as Yesterday had versions of both of these things before they went back in time).

Captain Underpants and the Sensational Saga of Sir Stinks-A-Lot
After using it once more to go to the future and recruit their future selves to help them fight Sir Stinks-a-Lot, George and Harold decided to keep the extra Robo-Squid Suit and leave the Yesterday version with Melvin, going on adventures while their Yesterday twins grew up and lived normal lives. The series ends with the duo first using the suit to try and rescue Crackers and Sulu.

Captain Underpants: The First Epic Movie
The Gigantic, Glow-In-The-Dark, Robo-Squid makes a brief cameo in the end credits