You can import Java Worlds to Wii U or Wii U to Java using PC Tools : 2 Converters = .MCCToolChest = Free but limited features .Universal Minecraft Tool = Pay but all features available. Nobledez : MC Wii U Map Manager + Tutorial
Post
Also PCK Studio for Custom Skins
Dude what a lifesaver, had been looking to back up my old worlds, tysm!!!!