In my opinion, many of those affects can be achieved quite reasonably on the Mega Drive given the right circumstances: - Rotating bosses/backgrounds. The background rotations are usually the platform on lava (which can be achieved via H/V-scroll manipulation given it doesn't rotate further than what looks to be about 30 degrees), and the wheel with those rhinos (which is a little more complicated, but has been done before, and luckily the background is black in the boss, so a plane is free for this). The bosses themselves are usually very small sprite sized characters, so some art rendering can be done for those. The final boss with the ship can be done on a plane using slit scanning for various widths, and v-scroll manipulation for various heights. - Ghost house transparency This one would be an annoyance admitedly. The ghost itself in the secret boss could be done reasonably thanks to the fact that it's in a fixed non-moving room, art/palette manipulation can achieve it, but the ghost house's mist would have to be simplified in some way. I am wondering if the shadow/highlight with sprites would be an acceptable compromise, I mean, not many sprites load on-screen at once for SMW right? - Keyhole transition This would normally be an issue, except for the fact that the level graphics are very primitive and to me they look like they use very little colours or the colours are extremely similar, what could be done to some great success, would be fusing the FG tiles currently displaying onto the BG in a free VRAM space, and then using the FG with H-blank V-scroll manipulation to mask off the shape of the keyhole. - Pixelated transition This is probably the easiest within reason, iirc didn't Pier Solar do something similar? At any rate, H-blank V-scroll manipulation again. - Music/sfx might not be perfect You'd be surprised, I am confident the audio can be replicated to the point where you couldn't tell the difference unless you were to hear them side by side.