Elyos03
↑↑↓↓←→←→ B A START
The only broken thing I see with Shadow is that he becomes visible again after jumping into the sparkles. This doesn't affect Silver, or any other character as far as I can tell.
The only problem I saw with Silver was a warning that appeared when I loaded into the bonus stage:
WARNING: ./Characters/Silver.wad|LUA_SSIN:189: attempt to compare number with nil
My Silver.wad was last updated on May 11th, so I'm not sure whether I have the latest version or not.
Regardless, these seem more like character issues than issues with the Bonus Stage. If you could give me more details about what problems you're seeing, I might be able to help more.
With Shadow, the Bonus Stage is unplayable like an broken level on Doom. With Silver, his script can... Break? anyways, https://www.youtube.com/watch?v=1Isjgc0oX0s