I would've liked something from Shadow in Brawl. But eh, whatcha going to do? I wouldn't have minded so much if they didn't make Shadow his own Assist Trophy.
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Also, not one multiplayer/battle them from the Sonic franchise was in Brawl. What's up with that?
Dark Dawn kind of sucked, imo. It had some nice improvements, but it had too many Points of No Return, and many of the characters were tacked on. Also, the Gaia Blade and the(I forget it's name, but it's similar) were only equippable by Matthew. Your female Earth user couldn't use either of them. Which was ridiculous.
And yeah, I could see an X costume. Similar to how Blood Hawk's is. It doesn't change anything but their clothing looks.