The E-X robot models are each based upon a previous ultra-powerful foe of the hedgehogs, one that once took a super form to defeat. The main point of this was twofold. First it showed how powerful Eggman’s “Chaos Project” (I hope you caught that reference in the first episode) really was, actually able to power such powerful mechs. More importantly though, it showed just how much Sonic and Shadow have grown under Chaos’ teachings, and how strong Chaos is to begin with. Shadow’s mech, the E-4X Blackdevil, was based upon the final boss of Shadow the Hedgehog, Devil Doom. The 4 in the model number refers to Shadow the Hedgehog as the fourth core-series 3D Sonic game, just as the E-1X refers to Sonic Adventure as the first, it being a mechanized Perfect Chaos. For those who don’t recall, “Artificial Chaos” is an enemy which first appeared in Sonic Adventure 2, and made a return for Shadow the Hedgehog. Little is known about about them besides that they were made by Professor Gerald Robotnik in the model of the real Chaos from Sonic Adventure. This is what Eggman was referring to in the previous episode when he mentioned that E-1X was inspired by his grandfather. All that E-1X is is Artificial Chaos brought to a more powerful extent.
As for the E-25X, its point of origin is Season 0. Originally, the plan was for that to be based on Solaris from Sonic ’06 instead, but that wouldn’t make any sense seeing as Eggman’s knowledge of Solaris was erased from existence. The next thought was Dark Gaia from Sonic Unleashed, but there are a few obscure reasons that I decided that wouldn’t work (forget Season 0, you may not learn about that until as late as Season 4). The 25 is another nod to Sonic’s 25th Anniversary.
– And until next time, remember to live and learn every day!