We don't need 2D characters in SRB2. The reason why? They don't work right in 3D mode. And most eight-directional characters work correctly in 2D mode, anyway.
These sprite sheets here present about a hundred problems, but let me share three of them with you that I can think of off the top of my head:
1. These are not your sprite sheets. You stripped the author tags from them so that people don't know who made them.
2. These sprite sheets were resized down by Photobucket. It is not possible to use these in their current form because the filtering has distorted the original pixels.
3. Using pre-made sprites such as these in character WADs is highly uninspired. Do we honestly need some miniscule Sonic Advance Sonic running around where there should be a much higher resolution character in his place? Not to mention, we've seen that sprite in about a thousand different places before? We don't need this kind of stuff in SRB2. It just doesn't work.