Aside from kyuubi,exe, orochi, devilhog and atrocious these are sonics base forms in the story

Semi forms ( the only ones in the story are semi-super and semi-dark)

Super sonic god

The omni form is his strongest transformation and all the forms sonic has in this point by using the crystals of light

Note: all this forms are not made by me. They are made by talented artists especially omni sonic  he is made by guardian möbius