Deliberate mistake: Regardless of where the position of the sun is or the shadows cast off the player and his buddy Pokémon, the Team Rocket Go hot air balloons always cast a perfect round shadow directly beneath them. No elongation or shifting due to the light source. This is obviously done so the player always knows when one is overhead, but it still is a mistake in how shadows work.
Deliberate mistake: Fish Pokémon like Magikarp, Goldeen, and Tentacool straight-up hover in the air when you encounter or battle them—even if you're on a mountain, street, or desert. Which just looks goofy, but it's an intentional design choice so you can catch and use water mons anywhere without needing an actual pond. Basically, they're floating in "invisible water" for gameplay balance. They "swim" in the air, complete with bubbles sometimes appearing around them or a splash.
