Interesting story you have there, still dont like to use other digital life forms in digimon lines.Hi everyone! New one here. Mercuremon is kinda my favorite antagonist/digimon character ever so I always figured what would be the best evolutionary line for him.
So basically in my headcanon the Warrior Ten haven't managed to split their powers in the Spirits but reborn as many digieggs scattered throughout Digiworld. One of AncientWisemon eggs gets corrupted by one of the many iterations of Algomon, resulting in the egg hatching into a Algomon Baby I. Somehow, the good spirit inside AncientWisemon data manage to stop Algomon growth and it digievolves into Monimon and then Mirrormon and finally, Mercuremon.
That's when the evil influence of Lucemon and Algomon corruption kick in, conflicting with the positive AncientWisemon data. Mercuremon then somehow splits into two and undergoes two different Chou Shinka: one focusing on his mutant side - Sephirotmon - , the other on his metal empire side - Biomon. Both are very unstable due to the data corruption, and goes on a rampage against one another and the Three Great Angels. Sephirotmon defeats Cherubimon and with its data Kyukyoku Shinka into Metamormon, while Biomon does the same with Seraphimon and into Black Seraphimon.
The two sides fights ferociously, feeding both Lucemon and Algomon with dark energy and miasma, until Ofanimon finally step in, making the light return into their mind and purifying their data. At that point, Metamormon and Black Seraphimon jogress into AncientWisemon, returning to his full glory and defeating the evil. From that point, Mercuremon can Warp Shinka into AncientWisemon and all the middle iterations at any time.