Instructions
Begin the game, and remove a single Pokemon from your party, leaving you with only five Pokemon. Travel to Mt. Mortar, located on Route 42.
Use the center entrance into Mt. Mortar, then use a Pokemon with the "Surf" ability to walk on the water in the entrance, and climb a waterfall at the back of the mountain. Follow the path at the top of the waterfall to the bottom of the mountain, where you will find Kiyo.
Defeat Kiyo's Pokemon, and in return, Kiyo will give you a Tyrogue. Since you only have five Pokemon, the Tyrogue is placed in your sixth slot.
Use the Tyrogue in battle until it reaches level 19, then check its stats. If its attack stat is lower than its defense stat, give the Tyrogue an attack-raising item, such as "Protein," to ensure its attack is higher than its defense.
Level the Tyrogue up to level 20. If its attack stat is higher than its defense stat at this time, it will evolve into a Hitmonlee.