you need either mocha or haxchi. you can exploit the system using the browser hack to get in the door. haxchi requires buying a ds game from the eshop. brain age is the cheapest, so I'd buy that. I use cbhc which loads haxchi at startup. as long as you don't do something stupid, it will work as intended indefinitely. stupid things are deleting the exploitable game, moving it, or formatting the system. if you want to do any of those things, uninstall cbhc first. I did this as my initial exploitable game was yoshi's island, but I got to the last stage in that, so I used brain age as my exploitable game. retail games won't require cfw. wii u usb helper will tell you which games do. it's basically anything eshop related requires cfw.
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btw, using wup will require cfw of some sort; otherwise, games won't be installed. I forgot about that query.