The Metal Sonic suit is pretty cool here. It fits in with the style of the game, while still looking "Metal Sonic Like". The left photo shows the turn-arounds & some close-ups for the textures of it. Why does the one above have green eyes, but all the others with red? You can still likely get the suit with Steam, although the promotion was done in 2012. You have to have also bought Sonic CD's re-release through Steam, to get it, though. This item was a celebration for the addition of Sonic CD to Steam.

Here is a Spiral Knights Tails' tails promotional item. ONLY if you bought the energy pack AND Sonic CD in your Steam account between January 19th and January 31st 2012 could you get the Tails tails accessory here. (So it's pretty exclusive) As these 2 characters show, the tails look like they operate pretty normally. The left photo shows the texture, which looks nice as well.