Object of this team is to get as much type coverage into as few pokemon as possible. Since the Battle Tower only allows three pokemon for single battles, I've decided on a Physical sweeper, a Special sweeper, and a wall/support pokemon. (I can only hope this configuration isn't a bad idea right off the bat. =/)
Item: Life Orb; Nature: Jolly; EVs: 4 HP, 252 Atk, 252 Spd
~ Close Combat/Brick Break
~ Night Slash
~ Psycho Cut
~ Stone Edge
First thing to decide on is what to use for his Fighting STAB. Brick Break doesn't sacrifice defenses and destroys enemy barriers, while Close Combat just has more power. Next, since Gallade doesn't get Shadow Claw, Night Slash is the next best thing for near-identical type coverage. Psycho Cut is his other STAB, and finally Stone Edge to beat Flying.
Item: Wide Lens; Nature: Hasty; EVs: 4 HP, 252 SAtk, 252 Spd
~ Hypnosis
~ Shadow Ball
~ Focus Punch
~ Thunderbolt
Very standard set; a fast and furious Special sweeper with a Ghost-Fighting centered moveset for good type coverage. Hypnosis also helps Focus Punch get the extra turn it needs.
Item: Leftovers; Nature: Impish; EVs: 252 HP, 64 Atk, 132 Def, 64 SDef
~ Wish
~ Taunt
~ Payback
~ Toxic
I'm not exactly the expert in building walls, but this looks like the best I could find for this guy. Wish is his basic recovery move, and Toxic for doing damage while stalling. Taunt and Payback work hand-in-hand for a STAB offensive.