Board Thread:Questions and Answers/@comment-19203513-20130914101051/@comment-19203513-20131009080036

15 is the limit for a 5* card normally.

To get to 20, you would need to fuse mags of the same skill (Dream Eater) for 100% chance of skill lvl increase, or another card with the same skill for a small chance (or if max lvl, 70, then 100% chance) of skill lvl increase. Unfortunately, there are no other cards w/ the same skill, and no obtainable magatamas for him, so you're stuck at 15 unless you get the same card.

I hope you understand. I can be bad at explaining, so let me know if you didn't understand anything.