GF Energy is Spiral EnergyEmbodiment of fighting spirit? Check. Allows fighting robots to grow to several hundred times their original size? Double check. Enables Combining Mecha to do their thing? More checks than I'd care to count. The Gotcha Borgs need human Commanders to lend them their Spiral Energy since, being Borgs, they aren't a Spiral race. Mega Borg presumably had a way of artificially powering them, similar to how the Beastmen ran their Ganmen on solar power.
G Black was created by the Death Forcce based on the data that had been stolen from G RedBut since they didn't have all of G Red's data, they had to improvise for the missing bits, leading to a few differences, such as the Laser Blade.