Some little crits below:
The pale spots on the thwomp rows are very distracting. It is difficult to make out the face because there is this noise present, so I'd try looking at that. Lower the spots or darken them, is my impression.
The shading between standard and "atomic" (large) boo is not consistent, with the former shaded below, and the latter shaded from the right. I understand that's how the original sprites are, but you might try seeing if you can correct that.
You can, if you feel like it, also try and make the shading generally consistent over all sprites. Some have multiple shades, some few shades, some are strongly shaded, while some are not shaded at all. It looks like a series of different games, which is accurate because of where the source material has come from. But if you want them all together in one sheet, you might think about this.
The pale spots on the thwomp rows are very distracting. It is difficult to make out the face because there is this noise present, so I'd try looking at that. Lower the spots or darken them, is my impression.
The shading between standard and "atomic" (large) boo is not consistent, with the former shaded below, and the latter shaded from the right. I understand that's how the original sprites are, but you might try seeing if you can correct that.
You can, if you feel like it, also try and make the shading generally consistent over all sprites. Some have multiple shades, some few shades, some are strongly shaded, while some are not shaded at all. It looks like a series of different games, which is accurate because of where the source material has come from. But if you want them all together in one sheet, you might think about this.