I don't remember when I first discovered this, but I've been following this for years (Some of you old timers may even remember me posting about it before.) There's a certain melody, I first noticed it in Mega Man 4.. it's brief, but I could swear it reappears in later games. To put it to the test, I've made Mp3 excerpts of the relevant bits (Although I've let them run longer, the tune should be identifiable in the first couple of seconds.)

This was the first (Chronologically) instance I've found of this tune.
Mega Man 4, Dr. Cossack's Stage 3&4.

The next two are both from the same game.
Mega Man 7, Junk Man Stage.
Mega Man 7, Dr. Wily Stage 3.

The next occurrence doesn't appear until years later.
Mega Man X4, Cyber Peacock Stage.

The final one is slightly different, but similar enough that I felt compelled to use it. It's almost the tune, except it stops halfway through. I hope that makes sense.
Mega Man X5, X's Intro Stage.

Now then.. what do you think?

I don't know.  The MM4, MM7a, and MMX4 ones all sound very similiar, but the MM7b and especially the MMX5 ones are a bit different.  A key thing to know would be if there's a common sound designer or composer among all of those games.

Really? I thought MM7a & MM7b sounded very alike. Try putting them both in a playlist, and then skip to the next one after only a couple of seconds.

I agree that knowing the composers/sound designers would help.

They do sound similiar, but they seem different enough to me.

I guess there are only so many stage themes you can write for a Megaman game.  Megaman music has a very distinct sound to it, regardless of the composer, but yeah, that repeated motif is pretty strange!  It is in all of those tracks, even if it's not the same exact string of notes.

Yeah, they're similar in that they're four of five notes going down the scale, but I think the similarities end there. The decension is never exactly the same, and they all tend to 'lead' somewhere else. Can something as simple as four/five notes going down the scale really be considered a theme, or even a tune? I hear similar 4-to-5 note chunks in unrelated songs all the time, and I just chalk it up to coincidence.

Can you tell I have no knowledge of musical terminology?

I hear what you're pointing out in each track, and could very well imagine a composer creating all of these variations from a common theme. I'm more apt to chalk it up to coincidence, but it's an interesting coincidence nonetheless.

I guess it would be considered a rhythmic motif.  I don't really know much about music theory, but it is a repeating motif, and the notes aren't the same, while the rhythm is, so that's what I'd say. 

I disagree. The notes don't have to be identical for the motif to be shared.

That's what I'm saying.  Depite the note sequence being different, it is still a motif based on the rhythm. 

Where we really disagree is that you think it's coincidental.  I don't think it is. 

No, that's not what I'm saying at all. The pitches do not have to be identical for it to be a melodic theme. As for intention, if rhythm was all that these passages had in common, I'd be even more apt to blame coincidence.

Unless they're all written by the same composer, I'd say the resemblances are purely coincidental. Megaman music isn't exactly known for its recurring motifs.

(Although once again, the NES track blows the rest of them out of the water.)

Wha? Mega Man has had plenty of remixes. OK, not in Castlevania quantities, I admit. But look at the number of times the stage introduction from the original game was used (2, 4, 7, 8, R&F, X1..)

Some more examples:
-Guts Man Stage, Snake Man Stage->Robot Museum
-That one stage complete theme that's in a lot of the games you know the one I mean
-Dr. Wily Boss Battle->Shadow Devil
-Mega Man Ending->Mega Man 2 Intro, Mega Man 4 Credits
-Zero's Theme 2->American X5 Intro, Zero cutscene from X6
-Dr. Light's Theme->Dr. Lights Theme (X5)
-Sigma Boss Battle->Eehh, it was in X5 also.
-Sigma Battle->Sigma Battle1 (X2), Final Battle(X6)
-Sigma Battle 2->..Sigma Battle 2(X2)
-Bubble Crab->Tidal Whale/Makkoin/Duff M-aw screw that.

And within the Zero Series is pretty obvious stuff..
-Infiltration->Infiltration II (Incidentally.. the Remastered version of II? Winamp says I've played this tune 113 times recently. Great, great tune. Love it. *plug*)
-Neo Arcadia->Neo Arcadia II, Neo Arcadia III
-For Endless Fight->For Endless Fight II, For Endless Fight III
-Crash I through Crash IV.
-Labo(Z2)->Labo (System-a-Ciel)(Z3)
-Sand Triangle->Sand Triangle II
-Departure->Awakening Will (It counts if it's in the same game, right? No? OK, that makes things easier on me then. *whew*)
-Cannon Ball->Cannon Ball - Hard Revenge

Also, I'm fairly certain different composers have remixed other composers works before. Example, example..

Ah yes, Theme of Zero from Mega Man X1 by Setsuo Yamamoto, remixed by Ippou Yamada in Mega Man Zero.

Also note I actually haven't gotten around to X7 or X8 so if I missed any from those.. yeah.

There's a big difference between a remix and a short motif that pops up in unrelated pieces.