Here is the info on comet & meteor:

Comet:
1.) damage=[1 ~ (vivi's Lv. + vivi's magic power)] x 56
2.) hit %: 67

Meteor:
1.) damage=[1 ~ (vivi's lv. + vivi's magic power - 1)] x 88
2.) hit %: depends on vivi's stats, but has confusing formula and do't feel like typing it because i would have to use parenthesis.

So, that's pretty much it. Just in case you get confusing, "~" means "to". So the number between the "[]" are randomly chosen within the range.