Actually, the thing that separates bellums eye from Majora's is the angle of it. Bellum isn't in the correct position that makes the fused shadow eye and Majora's masks eye so similar.
Also, Majora seemed to have most of it's power from the fact that it's owner was weak minded. Midna however...
Here's something for thought.
According to legend... the troubles caused by Majora's Mask were so great... the ancient ones, fearing such catastrophe, sealed the mask in shadow forever, preventing its misuse - Happy Mask Salesman
That story resembles another story doesn't it...