Hi! glad to see around ^_^!
As for the 'MEGA' Pack. It's usually a term used for 'large pack that contains all other packages / items.
Or, another way to look at it is a big bundle full of all the asset packs into one.
so in this case, it would hold all of the characters from both the knights, and mages, and all the other packs that you are selling!
I hope that clears things up!