Also(becuase im reading Hary Potter)

i finished the 6th one at the end of the vacation. it made me very curious about what will happen in the sevent, but whatefe.
like in harry potter, the book with the evil spells, if you could use those in DD <img src="/ubbthreads/images/graemlins/badsmile2.gif" alt="" /> cutting someone open with invisible swords, blood everywhere(ohh, that will be the most spectacular scene in the 6th movie of HP).

maybe you could add scrolls, like spells you can use once or a specific count.
like scroll of summon skeleton: the same effect as summon skeleton skill, just that you can use it once and it disapears or summon skeleton (level 3, 4): that would mean: the third stage of summon skeleton, and you can use the scroll 4 times.

but it are just ideas