In the last 2 episodes, when the Devil Colony Gundam makes its appearance, all the colony nations launch their Gundams to stop it. Among those in the battle are several suits from the shows prior to G-Gundam, including: the RX-78-2 Gundam from Mobile Suit Gundam, the GP-01 and GP-02 from Gundam 0083, the V2 Gundam from V Gundam, and the Wing Gundam and Tallgeese from Gundam Wing, which was in production while G-Gundam was airing on Japanese TV. The Crossbone Gundam X1 from the Crossbone Gundam manga is also present. Also appearing are the titular machines from three of Gundam creator Yoshiyuki Tomino's other anime: Zambot 3, Daitarn 3, and L-Gaim Mk-II. Show Zama & Marvel Frozen of Aura Battler Dunbine appear in the Neo Japan Colony as well.
The order that the 4 members of the shuffle alliance appear at the finals is the same order that Domon went after them in the beginning of the series.
In the third opening animation for the series, director Yasuhiro Imagawa can be seen in one of the Neo-Hong Kong crowds wearing a Star Trek uniform.
The Mammoth style Gundam seen beaten in Kiral's flashback is called Mammoth Gundam. According to most sources, it is from the colony of Neo-Siberia. It can also be seen as part of massive Gundam army that attacks the Dark Gundam in the final episodes.
The Dark Gundam is revealed very early on to be made up of DG-cells, which are essentially nanotechnology. Nanobots have long been considered to be the Holy Grail of Technology, which is an appropriate comparison, as the Holy Grail (depending on the interpretation of the myth) gives life and the Dark Gundam was originally designed to not be a weapon but to restore the decimated Earth in the anime.