Hey there, this mod has several issues that need to be fixed and updated if you want to continue making more mods for Mario Kart 8 Deluxe.
First of all, as many have stated, your rig needs heavy improvement. The problem is either your weight painting while not using a blend function especially apparent on the joints of the model (you have to paint weights with more than just 1's and 0's) or your placement of the vertices relative to Waluigi's bones. If you're using the CSV method, you have to delete zero weights before you can continue, which is accomplished by going to the weight table and removing zero weights. Some parts of the face look normal in your screenshots, but others look really off as a result of the rig.
Second, the normals need fixing. I don't know what method you used to import the model but you need to smooth those out so it faces the right way and your model lights up accordingly. The normals are at the worst in their hands, as they are shadowed rather than lighted up.
The emblem looks good and I haven't heard the voice yet so I can't critique that.
So, if you fix those, I can consider dropping a like on this mod, because I like the idea myself.