Mega Bomberman is scaled down graphically from the original PC Engine release - all graphics have fewer shades of colour due to the Mega Drive's 64 colour palette, usually rendering them in only flat shades (ground tiles noticeably suffer from this).
Likewise, the music has been retuned to work on the Mega Drive's sound chip. All the music is identical, except for Jammin' Jungle and Vexin' Volcano, which are given brand new music in Mega Bomberman.
New logo (with letters cannibalized from '94's logo) with trademark. "RUN BUTTON" is changed to "START BUTTON". "PASS WORD" has the unnecessary space removed. Copyright year is updated. The Louie is recoloured. All the objects are moved around to some degree. The Blue Bomberman is absent (since this version is only 4-player).
Bomberman doesn't shield his eyes when the Spirit Picture gets destroyed in the intro, nor is the sky whitened by the blast. In addition, Mega Bomberman plays the intro in fullscreen, but is widescreen in '94.
"ぱか (paka) is translated as "KRAK".
There are no Bombermen seen on the planet segments in Mega Bomberman; thus, there is no sequence of the cloaked monsters beating them up.
All the world names are changed; Mega Bomberman goes for alliteration (Vexin' Volcano, Thrashin' Tundra, etc) while Bomberman '94 uses word jokes (Morimori no mori - Morimori's Jungle). See the area pages for more details.
Bomberman '94 allows you to play through the stages in any order you want by cycling through them with the D-Pad. Mega Bomberman doesn't have this option, even though you still hear the same sound when pressing the D-Pad; you have to play them in order (though you can return to a stage you have completed).
Highlighting a stage in '94 will cause that part of the Spirit Picture on the floor to glow, and completing the stage will 'fill in' that chunk of the image. The Spirit Picture never gets filled in or highlighted in any way in Mega Bomberman until the boss of that world is completed.
The Japanese pause graphic has a sleepy Bomberman. He's wide awake for the English version.
Rather poorly represented by this GIF, but Bomberman '94 has various aquatic effects such as a rippling background, drifting bubbles and fish floating by in the foreground. Mega Bomberman ditches them all for technical reasons, it seems.
Likewise, the Japanese version has snow, but the English release drops it.
They mildly realigned things. Can you believe that?!
The Battle Game portraits are hit hard by the Mega Drive's limited palette. Green Bomberman was relocated to player 4 in Mega Bomberman, for whatever reason.
You can only see one stage at a time in Mega Bomberman. Palette issues, I imagine.
The Japanese version uses a cute image of a Louie in a sun hat as a pause graphic. The English release has no such pleasantry.
Mega Bomberman adds new features to the South Pole battle stage that aren't in the Japanese edition - the fireworks from Thrashin' Tundra are included (you can see the red bomber is seen being hit by a rocket in the screenshot), and placing a bomb in the centre of an igloo will give it a full-screen blast radius.
Mega Bomberman's crowd was made into a shower of whiteys.
Judging from text in the game's ROM (encrypted as simple ASCII - you can view it in something as simple as Notepad if you want), the Music Room was evidently part of the game's debugging options, alongside a boss select and a stage select. I haven't heard of any means of accessing these in-game, and as such I don't know whether they're still present or if this text is all that remains. It does provide us with names for all the bosses, though.
As of this writing, unused stuff has only been found in Mega Bomberman, thanks to having a fat stack of uncompressed graphics. Since I haven't found any way of accessing Bomberman '94's graphic data, I don't know if all of the following are leftovers, or were newly created for the SEGA release.
Props to the Oracle of Wuffing from The Shyguy Kingdom for ripping these graphics.
All of the player characters have these two-frame animations of them crying on the floor. My best guess is it was meant as a lose or draw animation - both scenarios just reuse the 'stunned' animation where Bomberman spins around on one foot.
Bomberman's unused animations. The first two are fairly nondescript, but the last few are interesting - sleeping and swimming! None of the other characters have swimming animations; my only guess is as a cinematic or something. The sleeping I assume was an idle animation at one point.
The girl Bomber adjusting her bow. Idle animation, most likely. Not sure what the last one is.
The punk with a guitar! Also, some sort of orange shape. Not sure what it is or if it's even related, but it's among his graphics, so there it is.
The elderly Bomberman using his cane to leap into the air. The middle frame is used for jumping onto a Louie. Were the players meant to have unique abilities?
Also, drinking tea.
Fat dude eating stuff. Big surprise!
The bookworm's victory animation has him throwing his hat off... in the sense that he grabs it and makes a motion of throwing it away, but his hat just vanishes. There's graphic for the hat! Also, an idle animation.
The second frame is used for jumping onto a Louie, but the unused first frame seems to imply the Bon Saver had a rocket dash of some sort. Who's to say?
He also has animation of tinkering with stuff behind his face. Kinda freaky.
Would you believe the dude with the pickaxe never actually uses his pickaxe in-game? Evidently he was meant to. We were swindled!
(you may recognise this because I made use of it for the "unfinished" graphic on this very site. Now there's trivia you can impress your friends with!)