So I messed around with the SMW style a bit and found some things that might be of interest. Some of these might be more obvious than others.
- Feathers placed on the ground will just fall through it.
- Goombas and Koopas (and Koopa shells) can still be flipped with the cape spin or while hit when standing on blocks, but Buzzy Beetles, Spinies and Bob-Ombs can not. I suspect this has to do with their new sprites, as they aren't 16 pixels tall and therefore would hover a few pixels above the ground if flipped.
- The Wiggler has a new body sprite that shows two of his legs, but it only appears in the editor. Weird.
- The Bullet Bill Blaster has a slightly different appearance. Rather than using two vertical 8x8 tiles for the top part and flipping them like the original game, it actually makes use of an unused 8x8 tile in GFX14.bin. This leads me to suspect that Nintendo actually went into the ROM to get the graphics rather than using sprite sheets or something.
- Similarly, big Mario's running jump sprite misses an 8x8 tile. This seems to further confirm that theory.
- Mario's shooting fireball sprite lost its extra pixel of hair. How they noticed that but not the missing 8x8 tile is a mystery.
- Mario can run past one-tile gaps without falling in randomly like he could in SMB.
- Holding the jump button doesn't affect falling speed any more.
- The spin jump is slightly lower while the normal jump is slightly higher. The spin jump also seems to be less floaty.
- The spin jump will now always give you a small boost if you hit an enemy with it but without holding the button.
- Climbing on vines horizontally will slow Mario down. Mario also now uses a new sprite for when he's on a vine but not moving.