Reserving for Waterwarrior
You'll need to give me the constraints for your scramble, though.
Edit:
You get WWarrior, the _____. That's right, you get to choose what Pokemon this is. Just pick something you like, it doesn't matter. WWarrior is absolutely obsessed with being as annoying as possible.
Firstly, no matter what it is, it gains a second ability in Defeatist. Except it's changed to "only use non-attacking moves when at 50% health or below".
Secondly, you must use WWarrior in each and every gym battle that is not being soloed, and using only WWarrior, force a Pokemon to use Struggle (or make them run out of PP, I'm not sure off Struggle exists in Yellow). Yes, every gym battle, trainers included, once per battle not per pokemon.
Thirdly, WWarrior must always be switched in whenever Haxmaster faints, because WWarrior is Haxmaster's greatest fanboy/girl (edit: don't know which, so choose the one applicable to you), even stealing inspiration for his suicide indulging scramble. Because it loves Haxmaster so much, WWarrior must solo the pokemon that fainted Haxmaster. If it fails to do so, throw out every item you have (not including TMs and stuff, just potions and balls and that sort of stuff). I'll throw you a lifeline here. If Haxmaster faints during its solos, you may bring in WWarrior, and faint the pokemon who fainted it. You may then continue the solo with WWarrior, on the condition that it can only faint Pokemon while under the effects of Defeatist. This doe snot count towards beating the third to last challenge.
Next, keep WWarrior 2 levels lower than Haxmaster, since WWarrior's always 2 steps behind. No more, no less.
To use an item on WWarrior outside of battle, it must first offer the same item to Haxmaster, and that item must be used on Haxmaster first (so if you wish to use a potion, use one on Haxmaster first, and if Haxmaster can't have a potion used on it, then WWarrior can't either). If in battle, you don't have to use the item on Haxmaster first (as that would waste a turn), but the item must be able to be used on Haxmaster at the time you use it on WWarrior.
(third to last challenge here) The final challenge? To prove its worth to Haxmaster (because to WWarrior, Haxmaster is Pokemon-god), WWarrior must solo a gym leader, and it must only faint Pokemon while under the effects of Defeatist.
When it's finished doing all this, it may finally consider itself equal to Haxmaster. Finish the game with them both at the same level post-Champion. If they are of different levels, too bad, restart from your last save and try again (so save before the Champion!).
Oh, and one final thing: since you sold your soul for Pokemon and not to Fluttershy (how can you say no to Fluttershy?), WWarrior must solo all wild pokemon who resemble real-life creatures (so Rattata counts as a rat, Pikachu counts as a mouse...practically all Gen 1 Pokemon resemble animals...humans are exceptions, so you can skip the Hitmons and the Machop line, etc.)