You've made it very easy to make your challange difficult, since you only have one pokemon. So I'll just jump down your throat on this one, k?Accepting Scramble for Ruby version.
- Only one pokemon, a Mudkip.
- Difficulty level as high as possible.
Brace yourself. You may not overgrind to keep yourself in the game. Therefore, you may not be at a level greater then 10 times higher than the number of the next gym. So your level restrictions are as follows:
and so on. The level 80 limit for Wallace lasts for the rest of the game, though you may level up past your set level during mandatory fights (such as fighting people to reach a gym leader, fighting Magma people, and the 5 straight battles at the Elite Four.
In addition to this restriction (which is a lot more brutal early game then late game), you may not evolve your cute little Mudkip. Ever. You can use all manner of X items, healing items, and Double Team trolling to make this task easier.
This IS possible. I shall send you a video link as proof: http://www.youtube.com/watch?v=TOpZOpcjVQA&feature=plcp&context=C4d8abeaVDvjVQa1PpcFPY4gbxVHg4sXdXWc-_sHqpmspfm0AlPrk=
This guy uses a Slakoth and soloes the entire game without evolving. What a boss.
EDIT: FUCKING NINJAS
Take the Absol who helps you during your run away from the village. This Absol is obsessed with ASB Combos, and thus may ONLY have moves that are linked together. Moves that are not linked cannot be used (you can manually set what moves it can use). Just a quick summary of how it can be laid out:
2 2-move combos OR 1 3-move combo OR 1 4-move combo
Additionally, this Absol must be on the front lines instead of sitting in the rear for every battle against a pokemon not obtainable in ASB. In ASB there is no hunger system, either, so after you get Absol you must soft reset the game every time you reach 0 belly, no exceptions. Otherwise you'll confuse the poor thing so much.
Finally, postgame (if you're even playing it), he catches on that this is a game about exploring. So send him through the Purity Forest, where you are only allowed to bring one pokemon with no items or gold, and they start at Level 1. At the 99th floor, you get to recruit Celebi with no boss battle whatsoever, but that's because the dungeon IS the boss battle. This challange is mandatory if you are playing postgame; if not, just ignore this part.