Bad Export for You: Until recently with the release of the whole Showa series by Shout Factory, Most Region 1 Gamera DVD releases contain awful, faded, little to no color Fullscreen 16mm TV prints, most masters actually stolen from the video catalog Sinister Cinema.
Dueling Dubs: About half the series was dubbed twice: First, by AIP-TV (The English Language Dubbers Association and TitanProductions did the actual dubbing) in the '60s and '70s, then later by Sandy Frank in the '80s, who used pre-existing Hong Kong produced dubs for at least Barugon and Gyaos. The first set of dubs are the ones that show up on budget DVD releases (the actual pristine film elements are currently stored in the MGM vaults); the second appeared on MST3K.
Hey, It's That Voice!: Many recognizable Hong Kong dubbers can be heard in the late '60s international dub used for Sandy Frank's syndicated version of Barugon. Ted Thomas (Kubota from Godzilla vs. Gigan) even plays a newscaster.
Keep Circulating the Tapes: Neptune Media's OOP tape of Gammera The Invincible is the only way the see the American theatrical version in widescreen. Shout! Factory intended to include this version on the Gamera DVD, but the UCLA, the owners of the print used for the Neptune tape, refused to offer it again for a new digital scan. Since Celebrity/Just For Kids never issued it on Laser Disc, the Hong Kong dub of Barugon, which was oddly not included on Shout! Factory's DVD, also shares this fate.
What Could Have Been: An unfilmed movie by the name of Gamera vs. Garasharp. Garasharp was a massive, cobra-like creature, armed with a sonic rattle and poisonous breath. The story ends with Gamera defeating Garasharp (naturally) and two babies emerging from her body. Just as the military closes in to destroy them, Gamera rescues them and flies them off to a deserted island, because he's the friend to all children, not just human ones. The film was scheduled for a 1972 release, but Daiei went bankrupt before they could start on it.
Examples from the rest of the series:
What Could Have Been: An anime based on the franchise was planned (rumor was that Cartoon Network was going to sponsor it) but was scrapped after Gamera: The Brave tanked at the box office in Japan.
Daiei had approached Toho with a proposal for a crossover film with Godzilla. Toho rejected the proposal.
Hey,Its that voice!: The english dub of Gamera Guardians of the Universe was made by ADV so...