Wow... Dimentio is owning... This battle would be the greatest magic show you would ever see... I think I'll go with Dimentio on this one. Although Beldam can lower Dimentio's stats and freeze him, Dimentio can make hundreds of illusions of himself (remember Chapter 8-3 in SPM?). I think if they were to battle, Dimentio would win.
"You think our rage a weakness? Then let me show you... how wrong you are!" - Edge, Final Fantasy IV