Wrong place to ask, this should be in emulation support. These GFX boards are for Graphic Editiing relevant posts, which normally have a releationship to Photoshop, Flash or any other image editing software.
I'll answer it anyway, and that is that no emulator emulates the GFX of Mario Tennis perfectly. So if your seeing plenty of glitches then that's just how it is for everyone, there is no way to fix this to be perfect, but you could probably make it a little better by turning on 'Force Normal Blending' & 'Force Depth Compare' which you can find under the advanced tab of your GFX Plugin Config. (Providing you've turned 'hide advanced settings' off, won't be the same for all emulators)
This will improve the GFX a little, but not enough to make it perfect, you should still be able to play the game alright though, but sometimes the ball might suddenly disappear, and certain courts the lines can be hard to see on, if ya want perfect GFX buy the real game, that's really your only option. But good luck for ya with the emulator ;)