What's the best stage counterpick for Fox against Marth? Consider my opponent M2K where if I get grabbed on FD I lose a stock, if you would.
Stadium is usually a good bet.
Cruise and KJ64 also give you a slight advantage.
Marth fairs well on neutrals. YS, FD, BF, and FoD are pretty favorable for him.
DL64 can be in your favor. However, if he grabs you enough, it's still very easy for him to win.
Is shine --> shorthop aerial useful for shield pressuring? It just seems to me that there is alot of room for error.
It's useful. I wouldn't worry
too much about mastering it if you're still somewhat new to Fox, but in the long run it will help you a lot.
If you haven't yet, you should become competent at waveshining first. It's easier anyhow.
What are some good applications for the f-air and d-air?
Don't worry about incorporating fair into your game really. It's not worth it. Just realize that nair >>>>>>>>>>>>>>>>>>>>>>>>>>> fair.
Dair is good on characters who are hard to uthrow uair combo and against people who tend to crouch cancel. In general, your opponent can not CC drill shines, so if you catch them CCing, you get a free waveshine upsmash / grab.
How to avoid Jigg's spacie combo? (uthrow - rest)
Pretty obvious: don't get grabbed. But everyone gets grabbed. Just try to DI it so that rest doesn't combo. At medium percents, always DI it away so that you die off the side and can respawn quicky enough to punish the rest with a charged upsmash.
Lots of Jiggs players will wavedash back and grab you when you nair. Try to nair farther than you would usually to counter this (if you have a good feeling the Jiggs is camping for a grab).
How do I effectively use d-throw?
It's not terrible against the characters who can jump out of uthrow uair. Mario, Doc, Luigi, and Samus are the notable ones. Most people will tech the dthrow, so if you feel they'll tech away from you, run forward and upsmash them out of the tech roll.
Should I use a waveshine against characters who are lighter then marth? (Tech chase maybe?)
I'm assuming you mean the characters whom the shine knocks onto the ground. It's always good to have someone knocked down. Their options are limited and your chances of following it up are high. You probably already know about thunders combo, but if not, here's an example of it.
http://www.youtube.com/watch?v=gIGVJFkVKCQ