Unsure if this topic has come up much in the past (so forgive me if this is somehow old news), but I've had this sitting in the back of my brain for quite a while. Spoiler: Sprite Comparisons My train of thought: Spoiler: Notes A few of Metal's sprites are heavily based on Sonic's. Shown here: idle (top) part of Sonic's water current floating | part of Metal's boost attack (bottom) Metal uses two slightly different running sprites ingame. Shown here: when Metal is in the lead... (upper middle) arms are bent down a tad hands are closed legs are pointed down + slightly back (implying low speed) chest is slightly puffed moves slow in game when Metal is behind... (lower middle) arms are raised out a tad hands are open legs are pointed noticeably far back (implying high speed) chest is rather heavily puffed moves fast in game (can roughly keep pace with a Sonic that's transitioned from walking to circle spinnyfeet mode on a flat surface, in my Time Attack testing) Looking at the ripped unused sprites (trusting the Spriter's Resource, as it has some that aren't even on our own wiki), you can see a lot of similarities between the "transformation" sprites and Metal's basic movement ones: Spoiler: Notes the Second These have been arranged according to my own eyeballs and noggin. Shown here: similar to upper middle... arms are bent down a tad hands are closed legs are pointed down + slightly back chest is slightly puffed seems to just be that one frame similar to lower middle... arms are raised out a tad hands are open legs are pointed noticeably far back chest is rather heavily puffed has multiple quill flowing frames (associated heavily with quick movement ala circle spinnyfeet mode) While not clear evidence of any purpose in particular... it's pretty clear to me that these sprites have at least something to do with each other. Were these always intended for a transformation for Sonic? Were they just reference guides for Metal's flight poses to be based off of? Who knows! Do we have anyone that's poked around in CD enough to see if those sets are called in any code, or is it still understandably unexplored territory?