I think the first two from the left might not fit too well in SMBX since they're based off of 1x1 pixel sprites while SMBX uses 2x2. Also, do you plan to include .ini files to configure proper hitboxes? If you plan to use the SMW Dino over Mario without them the hitboxes will be way off
About the playables, they're ok. The first two ones on the left have a lot of 1x1 pixels, and so does the SMB3 styled Kooper! But being off topic for a little, could you please put that huge Koopa Bros. image in your signature instead of adding it to every single post you make?
These playables are ok I guess ( maybe I could use this in an episode )... I would really like it if you add shoes to the fish, because it kind of looks weird if it's on the ground..