Quote Originally Posted by AlphaFox View Post
Overmeld basically forces materia into an item without it having a slot but at a severely reduced rate of success. I think the first overmeld is 45%, then 33, then like 20%? I rarely overmeld so I could be wrong on the percents.
The success rate varies depending on tier of materia trying to attach and how many already attached.

I don't have exact figures though for each variable taken into account.