No, this isn't Mega Man from one of the various spinoff RPGs, but rather everyone's favorite robotic vampire, the classic Mega Man 1-3 version. Since it seems that there's a Mega Man fandom at this site, I figured this might be an interesting thought experiment.
As is well-known, the trick with Mega Man is the order he goes through the stages- he starts off a wuss, and by the end he's got a whole arsenal of cool options stolen from defeated enemies. So judging Mega Man straight up in the DL is even more impossible than usual, because he starts off a Light and ends up Godlike.
So. The goal is rather: Construct an ideal "season" in which Mega Man wins every match and is ready to take on Godlike's finest in a Dr. Wily-style stage afterward. In other words, everyone knows that Mega Man is awesome given him draining lots of powers, but how awesome can you make with as few matches as possible, each winnable? Preferably 4 or less, given that's the standard RPGDL season, but longer chains are fine too. A random example season might be something like "WA:ACF Emma -> SH1 Alice -> P3 Chidori -> SO2 Claude," for an idea of what I'm thinking.
Note that this is a silly exercise with a zillion asterisks and caveats generated from being bored today. You've been warned.
So. Assumptions! The cast average is pretty easy, as Mega Man is in a solo game. Mega Man starts off totally vanilla, with average stats all around (and no charged shots from later games of the series). The only distinctiveness is that he has a ranged attack for when that matters, and he's mechanical type (damn you, Rikku and PS2 Josh). Uncharacteristically (but making things much simpler) our Mega Man sucks at jumping out of the way (0% base evade) but is surprisingly accurate (100% base accuracy).
Now. As for the "suck up the powers of the robot master clones of the DL" part. There's a bunch of ways this can be interpreted, so let me set out two broad ideas.
Interpretation A: Every enemy Mega Man defeats becomes a new "form" he can switch to as a free action on his turn. He can choose to start with whichever form he likes. Each of these duellers acts like normal, except they have their own unique MP (and SP, FP, etc.) stat bars, but share the same percentage of HP and the same status effects / stat buffs. That is, switching from Palom at half health to Auron would give you Auron at 50% Auron HP, not ~25% or whatever an absolute conversion would grant.
Pros: Easy to interpret, vaguely like the Persona 3 main character or RPGMon with a shared life bar and not losing turns for form switches.
Cons: Not very loyal to the way Mega Man works. Equipping the Hard Knuckle does not increase Mega Man's defense, and the Quick Boomerang does not in fact make Mega Man faster.
I think the Cons to this are pretty big, even if this is the easiest to adjudicate. Mega Man is always Mega Man; he just gets new skills and attacks from the robots he defeats, and it only adjusts his own abilities indirectly (Leaf Shield can be used for defense too, for example, but it's an "attack" that you actively use.). So let's try this one as well.
Interpretation B: Every enemy Mega Man defeats adds to Mega Man's skillset. Mega Man gets the defeated dueler's default physical attack (at the defeated dueler's power) and any active skills they had at their power (that is, skills which are "use this for your turn"). He gains no benefit from passive or defensive abilities (that is, passive = skills always on, and defensive = Fire Emblem counters, FFT Reaction skills, and the like that trigger on an attack). Mega Man's statistics are always dead average - HP, speed, defense, etc.
Example: Mega Man defeats Angelo. He now has some wussy physical attacks if he wants them and various magic spells. He doesn't have Angelo's 20% resistance to ice or his good base speed, but skills like Buff/Kabuff can still buff Mega Man's stats.
Example: Mega Man defeats Karin. By equipping her, he is *not* status immune and does *not* regenerate. He does get her Sword Arts, though, which function exactly as if Karin used them (fire or physical elemental, etc.).
Note that there are a lot of weird edge cases with this, but I feel it's closer to Mega Man. Does Yulie get her FP boost passive ability? (Probably not, though it feels weird since that's like a starting MP bar.) FF7 limits or FFX Stoic overdrives clearly never power up, but would an FFX Attacker / Strategist overdrive still be accessible? Beats me (though without the passive ability Triple Overdrive the point is likely moot).
A quick note given interpretation B. Since Mega Man is average speed, average health, and status bait, this implies that he will die without a turn guaranteed against certain speedy opponents (Celia, Rubicant, Dehuai, etc.). That's no fun! Everyone knows that Mega Man can do anything if he tries(*not actually true). So.
House Rule 1: The one passive skill Mega Man can acquire is initiative. If he can kill someone with it.
This applies only to interpretation B, of course; obviously Mega Man can get it already under A.
And oh yes, one other thing:
House Rule 2: Mega Man can't steal the skills of characters with ratings greater than 4.5. (Read: "in Godlike")
Logic? Mega Man doesn't get anything from the Dr. Wily bosses. Also some of these skills are not just broken but hard to interpret, and without this rule the trick becomes even more to to find a spoilable godlike and steal their skills. Originally I just wrote it as "characters in Godlike," but that unfortunately catches some cool but non-broken Heavy-upgrades like Tidus and Raquel.
I think seeing Mega Man builds without either one of these rule would be interesting too, so feel free to suggest options for that.
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Anyway, as a suggestion... for the Dr. Wily stage to test any builds you make against, if you're using House Rule 1, I'd recommend... let's see, Zophar, Fou-Lu, Belial (w/ 4D Pocket), Yuna, Sephiroth, and Lady. If you're not using HR1 and thus don't have initiative, then tough but beatable opponents might be Jade, Citan, Chaos, Profound Darkness, and Lulu.
So, see any good Mega Man builds?