Metroid Prime 4 - Obvious why

Animal Crossing U - This would definitely help boost a lot of units

Yokai-Watch U - Now THIS would save the Wii U in Japan at least. Like it would sell pretty damn amazing. (Yokai-Watch is selling better than Pokemon in Japan. Not sure if it will sell great in the west, but it would boost Wii U in Japan)

Pokemon Red/Blue HD remake - This would boost sales practically everywhere

Nintendo making a deal with Capcom to release an exclusive Wii U Monster Hunter. If it was Monster Hunter 5, it would no doubt boost a ton. Especially in Japan.

EDIT: I am not asking for what is possible, what won't happen, what might be possible etc. 

I am not asking if it would be better for Nintendo to save these for the Wii U's successor or not. 

All I am saying with this post is what the Wii U needs in order to be saved. Regardless of probability. 

1.Confirmed not happening
2.Sorta already being made but Amiibo based
3.Extremely unlikely to be made
4.Nope, won't happen unfortunately.
5.Impossible, unless the NX is handheld with WiiU like power, then it'd be cross compatible.

WiiU doesn't need "saving", it's already done what it's capable of: meh sales because of meh circumstances.

The answer to your title is, "nothing."

It would be better if Nintendo brings those to the NX as soon as possible. The WiiU has been labeled as "dead" already, there's no going back.

Errm, Yokai Watch is not selling better than Pokemon in Japan.

The Wii U won't be saved and that's unfortunate, but it's just the reality. At this point they need to spend their resources pleasing the current owners of the console and just prepare for the next generation.

A pokémon First gen HD remake on Wii U will never happen. All other stuff could help but I think even if they all get announced for next year it wouldn't save Wii U, furthermore none of those games can be completed and put on the market by the end of Wii U's lifecycle

Yokai Watch 2 Ganso/Honke sold 3.13m in Japan. Pokemon Omega Ruby/Alpha Sapphire sold 2.78m.

1. OR/AS is under-tracked.

2. OR/AS is a remake and YW2 is a mainline successor to YW. A more accurate comparison would be X/Y to YW2.

Yokai Watch 2 Ganso/Honke is a variation of Yokai Watch 2. So therefore, it is more accurate to compare it to ORAS than X/Y.

Yokai Watch 2 Ganso/Honke (a new game) sold 3.13m. Pokemon X/Y (a new game) sold 4.29m.

Yokai Watch 2 Shinuchi (a 3rd edition) sold 2.61m. Pokemon ORAS (a remake) sold 2.64m.