I do like the Half-dragon Ascendant, Mage. I would say that a new ability every level plus full spellcasting might be overpowered, but... well, first you have to be a half-dragon, and that's enough of a drawback as it is. The way you did SR and DR did kind of confuse me, though. Racial HD?
By the by, is there a list of MM constructs somewhere? The Power Rangers need a capstone ability... heh.