Shadow is sharp-witted, always on edge and has a strong sense of purpose, willing to accomplish his goals by any means. Essentially a dark version of Sonic, Shadow can match him in both speed and skill, and can use Chaos Control with a Chaos Emerald. While preferring to work alone, he has helped Sonic and his allies when needed.

As this comic starts right after Sonic Forces, I suggest going for a voice type similar to his VA in said game, Kirk Thornton. Here's an example: https://youtu.be/LSdn8Ww5QTU?t=1m