If you make yourself look like Sonic you can run so fast that people won't be able to make out any details on your character design. Just never stop running.
In all seriousness there are some good tips in here.
The one I use the most is detailing my characters' faces by making symbols appear like freckles or additional blush.
One way to make this look more natural is by using opacity. For a more detailed approach use the gradient looking symbols with the masking effect applied to them. This will allow you to fade out your symbols in a more natural looking way. These symbols can also be used to fake shadows. Fake it 'till you make it!