i doubt thats the original Machinedramon from the big 4 as it & kimeramon fused into millenniummon.
i figured that wasn't ken, but i wonder if thats actually gennai though.
it could be benjamin, jackie, hogan, jose, or illya.
It could be though.
Spoiler:
The entire Digital World got rebooted, so it would make sense if we saw some old villains. Though Alphamon and Jesmon(who is the final evolution of Hackmon so they are probably the same Digimon) fighting and the 8th Digimon all being together (Nyaromon was originally not there) means it is slightly different than before.
Also IMO that's definitely not Gennai. They could easily copy the appearance of Ken, so why not do it with Gennai too? Especially cause the digidestined will trust Gennai if he appears before them, and obviously that would give a lot of advantage to whoever the bad guy is.
And there is def going to be some deus ex machina for restoring the Digimon's memories, cause honestly nothing will be the same otherwise, and having them befriend each other to the point they can reach an entirely new mega form in 4 episodes would be silly. Also Meicoomon still has her memories.
Also IMO that's definitely not Gennai. They could easily copy the appearance of Ken, so why not do it with Gennai too? Especially cause the digidestined will trust Gennai if he appears before them, and obviously that would give a lot of advantage to whoever the bad guy is.
And there is def going to be some deus ex machina for restoring the Digimon's memories, cause honestly nothing will be the same otherwise, and having them befriend each other to the point they can reach an entirely new mega form in 4 episodes would be silly. Also Meicoomon still has her memories.