Glass Goth is the main antagonist in Chocobo's Dungeon 2. He is battled several times in the story. As the final boss, he possesses two forms which must be fought with no pause in between.
Glass Goth is initially introduced as a villain from the future, where he has supposedly wiped out humanity, who has traveled into the past and is somehow connected to the Mysterious Dungeon, also originating in a future time. However, as the story continues it is eventually revealed that Glass Goth is not exactly what he appears to be.
Early on in the game, Mog discovers a large crystal within the depths of the Mysterious Dungeon. At the time there is also a Guz present, whom Mog threatens and chases away. With help from Bahamut, it is eventually explained that after being forced to leave by Mog, the Guz returned, hearing a voice from the crystal that apparently promises it anything it desires. The creature asks for power, the power to defend itself, and no longer be "picked on", and so begins a process in which the Guz evolves into Glass Goth.
As such this places Glass Goth in the future, but his connection to the past allows him to return to that time, even when Shiroma attempts to send him, the dungeon, and herself, back to what is initially perceived to be their own time. The negative feelings of this Guz are also named as the cause for the behavior of the villagers and the presence of the Mysterious Dungeon itself.
After being defeated at the end of the main story, Glass Goth returns in his original form but appears to be unable to maintain it. Eventually, it takes up residence in the doll Shiroma created earlier in the game instead, becoming the new character Kuz, who is available for use in the revived version of the Snow Mountain Dungeon as well as being a selectable second character for the secret dungeon if the player decides to participate in the Bonus Mode. As a party member, Kuz has low HP and weak physical attacks. He can, however, shoot a beam at enemies from a distance which morphs him into that enemy for a limited period of time.