The only game that can "save" the wii u is mario maker, as it seems to be the best gamepad centric game, with a huge ip, with a big concept of player creation. However, by "save" I mean on track to be more than 3/4 of gamecube'a lifetime sales. At this point nothing can make the wii u catch up to Xbox one let alone ps4
Animal Crossing has sold more than Smash in Japan and almost WW. Smash Wii U was at a disadvantage due to a 3DS version being released. It would have another 2.5m sales or more if there was no 3DS version.
Metroid would give a boost in NA and Europe. Not a huge one, but good one.
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