Ok, mudslide training is where you put 2 of your Pokémon in the Daycare center, where they will gain 1 experience point for every step that you take. Then, you go to one of the mudslides that you have to run up at full speed on your Mach Bike. Now, you just ride your bike up to one of these mudslides, and put your gameboy on the battery charger, and put something heavy enough to hold down your "up" button on your Gameboy's directional pad. Your character will keep going up the muslide and then sliding back down it, causing the Pokémon in your Daycare to level up. Of course, Pokémon in the Daycare will not gain EVs, so you will want to make sure that your Pokémon are EV trained before you do this. Also, the mudslide trick only works in Ruby and Sapphire, it will not work in Emerald. Ninteno disabled this trick before it released Emerald, and your game stops counting your steps and awarding exp. points to the Pokémon in Daycare after you take a certain amount of time in one direction.