Ghastel is the leader of Lucifer's demons. Ghastel can fly by creating a dark clouds beneath both his feet. He attacks Krillin and Goku and eventually chases them through the cavernous area, but is killed when they trick him into being eaten by a swamp monster. Dragon Ball Wiki
Android #13 (?l?¢?l?Ô13??, Jinzoningen Jusango?) is the thirteenth android in the series of androids built by Dr. Gero. He resembles and sounds like a redneck. He was built along with androids #14 and #15 with the mission of killing Goku. He "evolved" into the much more powerful Super Android #13 after absorbing key components from the defeated Androids #14 and #15. He was killed by Super Saiyan Goku fueled by a Spirit bomb. Only the fact that an Android #13 was created, but deemed a failure and subsequently destroyed was mentioned in the manga. However, since Dr. Gero's computer was still building 13 while 17 and 18 were active, it can be assumed that he was not entirely destroyed but stored away as a back-up plan.
A blind hitokiri working for Takasugi. He seeks to destroy everything in the world, similar to Takasugi. His level of swordsmanship is such that he can slash an opponent without the latter seeing him unsheathing his sword. However, Nizou's sword was broken by Gintoki during their initial encounter. Nizou later returns and severely injures Katsura and Gintoki using a demonic sword, 'Benizakura' which transmogrifies his arm and fuses the blade with it. The Benizakura acts like a parasite, slowly taking over Okada's body, which causes him to eventually become nothing more than a crazed monster. Due to the sword, his body has undergone several modifications. He later reveals that his entire upper torso has similar cybernetic modifications. He is eventually defeated by Gintoki. Though his fate is unknown, he is assumed deceased due to the effects of the Benizakura. His name is roughly based on one of the hitokiri of the Bakumatsu era, Okada Iz�.
Teacher/mentor to the Old Jouishishi members in their youth. Trained Sakata Gintoki, Katsura Kotarou, and Takasugi Shinsuke in swordskills and the bushido. He died before the Gintama storyline started.
Thundercracker claims the skies as his arena. He looks down in contempt on those who cannot leave the ground — he considers them lesser beings. He will often attack the flightless beings below him for no other reason than to satisfy his scorn. His superiority in this realm is the only thing he is sure of. Thundercracker is not entirely committed to the Decepticon cause, and even has some seemingly contradictory sympathy for the humans they terrorize. Fear of retribution from Megatron and the influence of his peers is usually enough to bury these doubts. Regardless, he needs constant reassurance from Skywarp and Starscream (which occasionally take the form of threats) that he's where he needs to be. Sometimes, his heart's just not in the job. In the early days of the Decepticon (Destron in Japanese version) rebellion, Thundercracker and Skywarp both faced the powerful protectors of Cybertron's cities, the Guardian robots (Japanese version is known as: GADEP - Groundling Auto-Destruct Powerbroker). According to Thundercracker, he was often not very successful. Thundercracker was one of Megatron's elite warriors, participating in the attack on the Ark (Iacon Bridge in Japanese version) and joining the rest of the Earth-bound Transformers in their several-million-year nap under an inactive volcano. He awoke when the rest of the Decepticons did, and took part in their attempts to gather energon and escape the planet Earth. (Source: Transformers Wikia, edited)