I'll have to go back and check out sonic, I used to have the first sega genesis as a kid and played the hell out of it. I had saved and went to buy a nintendo but they sold my dad and I on a sega genesis as it had just come out. hehe
I was thinking of bonus levels like that rotating one full of coins you try not to fall out of.
I was watching this old mario quickplay repeatedly with my notebook, I need to add enemies and was planning on using insects or worms and caterpillars in place of their gumbas. What I've been thinking with the pig is similar to gameplay as yoshi without mario with elements of a sonic world, so you can eat the insects, jump on others, etc