Yu - Gi - Oh ! GX - Episode 120 " Inter - Dimension Detention " , known as " Battle in a Different World ! The Gem Beasts VS Harpie Lady " in the Japanese version , is the one hundred and twentieth episode of the " Yu - Gi - Oh ! GX " anime . It first aired in Japan on January 24 , 2007 and in the US on September 22 , 2007 . Summary . After his narrow victory against Thelonious Viper , Jaden Yuki and co . arrive in an alternate dimension that ' s ruled by Duel Monster Spirits . The main building of Duel Academy was also transported there . The dorm buildings appear to have been left behind , however . Jesse Anderson ends up using " Crystal Beast Sapphire Pegasus " to fight off Harpie Lady . They determine that they can materialize their monsters using their cards , duel spirits are solid , and that everyone is able to see them . Although Jaden and Jesse are used to begin surrounded by spirits , they appear to scare all the others students and are therefore surprised when Sapphire Pegasus and Winged Kuriboh materialise . In addition , the basic rules of Duel Monsters , appear to apply , as Sapphire Pegasus with 1800 ATK was able to destroy Harpie Lady with 1300 ATK . Adrian Gecko escaped from the collapsing lab with Devil Arm in tow . At the suggestion of Jesse Anderson , Dr . Crowler and Vice - Chancellor Bonaparte gather all the students in the gym and tally them . They determine that a total of 100 students were transported to the alternate dimension , and the rest ( presumably in the dorm buildings ) , were not . Ms . Dorothy reveals that they have only one week ' s worth of food and water to ration . Along with the duel monsters problem , many of the students start to panic which leads to Jesse taking charge again and losing his temper with them . Once order is restored , Adrian arrives warning them someone is approaching Duel Academy . Bastion Misawa arrives in the desert , and is attacked by Harpie Lady . He ' s saved by Adrian , while Jesse attempts to fight off the Harpie once more . He ends up facing " Harpie Lady Sisters " as the first Harpy was able to use magic similar to the " Elegant Egotist " card to multiply itself . Rather than destroying Sapphire Pegasus with an attack , the sisters are able to continually attack him until he collapses to the ground , wounded . It appears not all of the usual Duel Monsters rules apply though , as " Crystal Beast Topaz Tiger " is able to destroy one of the sisters without affecting the other two . Though Jesse defeats the sisters , they discover that the Bio - Band s are still active , and thus Jesse has some of his energy drained . Bastion is taken to the infirmary , and he explains that after seeing Jaden ' s duel with Dr . Eisenstein , he became Eisenstein ' s assistant and helped him study duel theory . They developed a theory of their being twelve separate dimensions in which Duel Spirits reside . In an experiment , something went wrong and Bastion ended up being transported to the same desert dimension as Duel Academy . Meanwhile Blair , Marcel and some other first - year students are hiding in a classroom , afraid of the duel spirits . Blair and Marcel head off to find the bathroom , unaware that they are being followed . Back on Earth , Chancellor Sheppard has arrived back on Duel Academy ' s island and is shocked to simply see a crater where the main building should be . He is suddenly attacked by Echo . He is saved by two of Maximillion Pegasus ' bodyguards , who have also just arrived via helicopter . Pegasus explains he received an urgent message from KaibaCorp . Adrian gets back to the room where he had locked the Devil Arm in and discovers it ' s disappeared from it ' s capsule . Adrian determines that it found a more suitable host , someone with a great darkness in their heart than Adrian himself . The demon is shown , still taking the form of a glowing Pierce , searching . Yubel determines that Marcel Bonaparte would make a good host , and possesses him . Under her influence , he attacks and wounds Blair Flannigan , who is found in the hallway by Jaden later . Marcel is shown with the Devil Arm in place of one of his own . Featured cards . The following cards appeared in this episode . Cards in italics debuted here .