Hey SouthCraft, not to be completely off-topic, but your avatar, that gif of Kirby with the gun (Really funny. XD), is that from an episode from the TV series? Or did someone just randomly make it for lols?
I might be wrong but I think it's from a show called "Kirby right back at ya!"
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Couldn't you just resize and recolour a Chaos Emerald model?
I was thinking the same thing, the Master Emerald is just a huge Green Emerald. Btw, unless you talk about the Comics version where, if i'm not mistaken, Knuckles took a bit of the the master emerald energie to turn into this :
Super/Hyper Knuckles (the original from Sonic 3 & Knuckles) got his power from the Super Emeralds which are identiacal to the Chaos Emeralds but are much larger (but still not as big as the Master Emerald).