I've been working small bits on a Fighter's pass 2. Albeit, with two hard rules; Character 6(as in challenger 6 overall) needs to be a head turner, and personal favorites as well. While I am picking ToyAgumon over Agumon in this case, I still want to see Agumon in as is(as Toy would be lucky to be a Spirit, respectively. An alt costume doesn't work that well).
I also would prefer they focus on multiple seasons for the Final Smash. For Agumon, he has multiple Megas due to that, but I'm thinking either to use Omnimon(with a Triple Warp Digivolve term used, probably using the Savers' style animation because it's a bit faster than Adventure Warp Evolution) or stick with WarGreymon. I've noted the Digiegg thing too, but that doesn't work that well anyway outside of implementing if if you have a regular digivolution system as his mechanic. Another thing is WarGreymon could have colors based upon your costumes too. There's enough variants to count. You could do small changes like giving it slight recolors on small pieces of its armor to represent the Savers versions of Agumons. You can make some unique colors like Blue/White for SnowAgumon's warp version.
For instance, let's see the costumes are Agumon, BlackAgumon, SnowAgumon, Agumon(Savers), BlackAgumon(Savers), SnowAgumon(Savers). The first three are straight recolors. The last three mentioned just have slight variations on their armor, like small strikes or something. Then the rest is whatever costumes you can find. You could, say, have Agumon Hakase and Nise Agumon Hakase as the final two. They could go into variants otherwise. Maybe use VictoryGreymon for Hakase, but with no actual differences for the cutscene attacks. The sword wouldn't necessarily be used. Nise could go into BlitzGreymon, who might be easier to work with.
...Yes, I can't think of easy 7th and 8th costume. Though I admit there's also BushiAgumon and SantaAgumon. Same FS variants as above, too. Bushi is a swordsman, fitting VictoryGreymon. And Santa has "presents", which fits BiltzGreymon's bigger gatling arms a bit closer.