Flubber is a manifestation of Getter RaysIt's green, sentient, physics-defying, has the ability to split and recombine itself, shows an interest in mimicing humanity, and is used as a source of power for vehicles. Not to mention it was let into the world by a Mad Scientist.
The Getter is responsible for the creation of SparksIt spreads to new realities by influencing their inhabitants until one of them succeeds in creating a Getter Robo. Its pilots may also be Sparks, given that the few who can bring out the full power of a Getter tend to be mentally unhinged.
All versions of Getter Robo exist as Alternate Universe versions of each otherBased on the endings of New and Armageddon
Alternatively, what we seen at the end of Armageddon were:Previous incarnations of Getter Robo, including some we had never seen. Some bits of dialogue seems to support that.
Getter Rays are emitted by a G-Stone.Green, fuels a Super Robot and makes it even stronger when the pilot goes completely over the top? Of course. Coincidence? Probably not.