That question comes up fairly often, and... well... Brawl runs through a boat load of styles. As long as the characters look like they belong in that environment then it works out pretty well. That's typically accomplished through lighting and character shadows though oddly enough.
*This post was meant as a joke, not as an attack on my dear sweet @
Nefnoj
Also, super koopa is just from
Super Mario World. I haven't seen a Super Mario World styled one in 3D so I made him and wanted to include him in the stage. The hills in the background and the moon 3-up were mostly a nod to Super Mario World, and so I figured a few super koopas swooping through the background would look nice.