Ridley (Metroid)
But he's too big!
Value - A - Fits the villain role for the Metroid series, which isn't oversaturated either.
Effort - B - Has a model in game... but he's gonna be a lot smaller. There's quite a bit of
custom PSA work which can be used for some inspiration, at least.
Background/Reasoning - First of all, the size argument is pretty BS. Captain Olimar and Bowser already show that.
Ridley has been shown to be only slightly larger than Samus at times, so shrinking him is fine. Anyways, Ridley is a recurring boss in the Metroid series, and is the most frequent and recognized enemy in the series. Most people here know who Ridley is. After all, he is a boss in Brawl too... Oh yeah, and he just happens to be one of the most requested characters ever since the Brawl speculation days.