Hello ,
I would like to talk about the chance of success while upgrading heroes . It says 80% when you try to upgrade heroes and the drop chance of devil's soul is too low . So my suggestion is to make the chance of success 100% because it takes long time for devil's drop to drop , personally i spent more than 1 month to see devil's soul drops and when it dropped the upgrade failed . In my opinion , it's better if you change the drop rate of devil's soul or the chance of success.
Share your opinion !