The Official Hyrule Warriors Thread - Extensive FAQ Inside, Rupee Glitch Explained

[NinjaguyDan]

Last night I discovered something really helpful. Using the special attack for the kill against playable characters greatly increases your chance of getting their gold material. It may work for the strong enemy silver drops as well, I haven't tried those yet. No need for the material master potion. (but I did have materials+ on my weapon)