If there's one Pokemon that I hope gets some touch-ups to its model if it ever comes back in S/V, it's Yanmega. I love it's design very much, but it's easily one of the worse transitions to 3D that doesn't get talked about too much.
Let's take a look at Yanma/Yanmega's BW sprites:
Incredible active and always mobile and zooming around, very fitting considering they are speedy little dragonflies. Yanmega even looks
more mobile than Yanma, which is why the transition to 3D is gonna hurt it even more.
Yanma's 3D model is this:
Not quite as fast as Gen 5's, but still moves around, even does the head turn once which is a neat detail. Overall one of the better models especially for one introduced all the way back in Gen 6.
Yanmega, however...
Dude went limp. Yanmega definitely suffers from the flying model syndrome where they just float in place (like Xatu and Salamence) but it stings here a lot more because it's just NOT supposed to float in place. Its Dex entries constantly talk about it flying at high speeds which is reflected in it's B/W sprite very well, but here it just doesn't work. Even then, I can't say Yanmega's model looks bad, cause it's Yanmega. Yanmega just cannot look bad cause it's really cool, but it's definitely one of the bigger disappointments coming into 3D. With some models seeing revisits from GameFreak in Gen 9, there's a non-zero chance, however small it may be, that Yanmega can be improved. Of course, that's a big if it even comes back this gen. (Absent in Gen 8 too btw, this line does not get a break!)