Anything that involves ripping is illegal. There is no way out of this. Those games do not share their models or sprites for free, people reverse engineer to get those stuff to their original non-cooked self and share around. That is illegal. As many people tried to warn you, some companies do not care about how awesome your game is. They don’t like it when you use it. Hasbro is another example. Good luck doing ANYTHING with their MyLittlePonies.
The way hedhehog look might be suspicious though. An almost-sonic looking hedhehog is still dangerous. On the other hand, platypuses can’t be copyrighted due to being too awesome, go for it!