After completing through each of the 3 levels of each world, you get to the boss of said world and you're only allowed to use the basic charger.
Rewards:
First boss: Squid Hairclip
Second boss: School Uniform
Third boss: School Shoes
Fourth boss: Squidball Minigame
Final boss: Hero Charger Replica
The normal levels are just money rewards that slowly increase the further down you go with the last one being 2000 c, it's like going through half of story mode again with each amiibo.