I think the 13 darkness is..
1 Master Xehanort
2 Young Xehanort
3 Xemnas
4 Ansem
5 Isa
6 Braig
7 Vanitas
8 Riku Replica or Dark Riku or Data Riku?
9 Terranort ?
10 Apprentice Xehanort?
11 No Heart?
12 Eraqus?
13 ..Originally this was Sora, but he failed, so probably another...