Note: I am not responsible for bricking your Wii U.
This guide is for Tiramisu or Aroma Users
Here on this post, I’ll be giving solutions on how to fix these errors below.

1. Couldn’t find NUSspli file on the SD Card
Tiramisu:
Make sure you have NUSspli.rpx in sd:/wiiu/apps/NUSspli/ .
Aroma:
Make sure you have NUSspli.wuhb in sd:/wiiu/apps/ .

2. Unsupported Environment
Switch to an environment that NUSspli supports, if you are booting NUSspli from a supported environment but is still having this error, follow these steps for your environment.
Tiramisu:
1. Go to https://tiramisu.foryour.cafe , click on Download Tiramisu, extract and copy the contents of the .zip file to the root of your sd card overwriting existing files, reboot the Wii U and try again.
2. Switch to a different environment that NUSspli supports and boot the one your environment uses.
Aroma:
1. Switch environment

3. snip

This is all the errors that I could solve. Any other errors that are not listed here can be fixed if you ask on NUSspli thread or on GitHub.

 

[EggnogBoi]

I was installing super smash bros for the Wii u on nusspli and I installed it 3 times so far and everytime it tells me to check my power to the USB what should I do

 

[Korozin]

I was installing super smash bros for the Wii u on nusspli and I installed it 3 times so far and everytime it tells me to check my power to the USB what should I do

If using a Pen-Drive, then.. don't? Best I can say for that one, tbh.

But if you're using an HDD, then make sure it has a proper Y-Cable and / or power supply if it needs one. The Wii U is pretty picky when it comes to recognizing, sustaining and keeping HDDs in use.

If all else fails, you could just disconnect your USB Device, install the game to Sys Memory, then transfer it to the USB Device. I don't really recommend this because it'd be better to not wear out the NAND, but it may work.

 

[KeeperCP1]

If using a Pen-Drive, then.. don't? Best I can say for that one, tbh.

But if you're using an HDD, then make sure it has a proper Y-Cable and / or power supply if it needs one. The Wii U is pretty picky when it comes to recognizing, sustaining and keeping HDDs in use.

If all else fails, you could just disconnect your USB Device, install the game to Sys Memory, then transfer it to the USB Device. I don't really recommend this because it'd be better to not wear out the NAND, but it may work.

You hate pen drives? 😡
I have downloaded Smash Wii U on a 32gb pendrive

 

[Korozin]

You hate pen drives? 😡
I have downloaded Smash Wii U on a 32gb pendrive

I never said I hate them, but it's just an objective fact that they should not be used on the Wii U Console. The amount of writes, and large data stacks transferred usually ends up with the Drive being rendered unusable after a certain amount of time. Not to mention the fact that the Wii U will also at random cut power to the Drive, even while under active use which can result in crashes, corrupted data, and other undesirable behaviors.

If you want to use a pen-drive, then by all means, go ahead. But if you want data security, and sustainability, then a pendrive is not the way to go.