Where is the best place to level up? Go to werehog stages that have quite a few enemies that can be beaten via critical attack (egg robo/shooter/knight, Nightmares etc.). A nice long stage is the best place. The best places are ones with Dark Titans, for they give off the most exp (and the most points-40,000) when you successfully critical attack them. Skyscraper scamper (it has two dark titans, but very dangerous) and Arid Sands (has quite a few enemies), are ideal places. But the best place is Eggmanland. It is not uncommon to have 2700+ exp (each full bar is 100 exp) when you leave the level.
To unlock the werehog you must beat the first level to play as him thn he will be avalible sonic and the werehog take turns playing as each other so on the second level thw werehog will apear and you can play as him Have Fun!!!!!!!!!!!!!!!!!!!!