You shouldn't rely on video tutorials to get things modded, for your information. Things are always moving in the hacking scene and videos get dated quick. Just stick to the text guides, but always pay attention to the dates stuff is published.
There are good mods on GameBanana such as Waluigi over Captain Falcon, Mr. Krabs over Wario, and I've made some funny voice mods and all but I haven't shared those. If you want one-slot voice mods, though, beware of mirror matches, they tend to mute the voices. There's a fix for the Wii U versions, but I haven't seen tools that fix the mtb that governs one-slot voice effects.
https://gamebanana.com/games/5683