There are two skills. Excorsim is the first one and you have to get all level 1,2 and 3 weapons (DLC doesn't count on the 3DS) to unlock the first skill which requires 10000 ko's. The sec skill (25000) is unlocked when you collected all level 4 weapons (again, DLC doesn't count on the 3DS). So...
In the 3DS version the Boss Rush and Challenge Mode isn't available. So you have to defeat the Giant Bosses in either the Story or Adventure Mode. It can be tough, especially with Beast Ganon and Phantom Ganon. But like you said, in TP Map you'll get rewards twice when you kill a...
In Hyrule Warriors/Legends we're able to collect material (endless gringing) to improve our warriors. But sometimes collecting all material for the warriors take ages because of certain Giant Bosses who are everything BUT loyal by giving us the material we need. So I can understand some people...