As you can see, unlike Sonic:

1. Fake's eyes (or...eye?) are/is overlapping his muzzle a bit and a bit bigger

2. Fake's head is slightly bigger

3. Fake's spikes are shorter

4. Fake is slightly taller than Sonic

5. Fake has a monster form

6. Fake's body seems to never age (As seen in the Modern Sonic, second picture, Fake's "modern" self remains the same as his "classic" self. Even when Fake is 150 yrs, he still remains the same as that.)

Here's the Pixel/First version