To avoid random battles, save your game about every 20 steps. This will reset the game's random seed, which also resets when your next random encounter will be. Now you can go through the entire 'Net without running into a single fight, or resetting your system because you got into a fight!
Once you beat the normal Navi decode this AJEKDUR2437561 and put it into the Staff Code window.
In multiplayer, Dark users are very tough because they become the Darksoul when you reduce them to 0 hp. However, if you use a chip or PA that freezes time and deals many hits, you can kill them without allowing them to become the Darksoul. A great example is the Pile Driver PA. Hope this helps you take out those cheap Darkies!
The Save Icons are as follows: