You're both cats with terrifying stare faces.
I guess if you wanted to be offensively gross, you could also have the custom character be more like an actual Sonic OC, giving the creation a sick fetish or excessively terrible appearance to creep out both modern and classic Sonic. Male pregnancy, both kinds of genitalia, multiple arms, super muscular and/or morbidly obese, multicolored hair, Heterochromia with unusual pupils, a strong desire for vore... yeah, that would be the sort of original hero a true fan of the Sonic series would want to have in Forces.
Phronemophobia
^^^^^^^
Listen to the cat. He's your ally.