OK, Darth, since it looks like you have a full team of earlygame mons at this point, you get Angel the Absol (preferably female). Angel is actually an angel in training, on a quest to achieve enlightenment and earn her wings. She joins your team to learn the ways of the world. She does not believe in fighting hand-to-hand; she only wants to use the supernatural abilities bestowed upon her by Arceus. Despite this, however, she honours the warrior's code of honour, which dictates that underhanded and devious tactics shall not be used. Finally, Angel believes that to achieve nirvana, she must be free of all artificial influences that may corrupt her soul.
Unfortunately, it is impossible for Angel to earn her wings, because this is Emerald and so Mega Evolution doesn't exist. Angel never gives up hope, though; once your party reaches the final hurdles, she goes on to defeat all other Pokemon that wish to earn the secret of Mega Evolution, to prove once and for all to the higher powers that she deserves a Mega. At last, in the battle against Steven, she transcends her physical form and goes on to the next world...
Now to put that into actual rules:
-Female Absol named Angel (can be Male if you have Absol-utely bad luck with genders and the 5% chance)
-Can only use Special attacks
-Cannot use status moves or moves with guaranteed extra effects (To clarify, Ice Beam and Fire blast are fine but Thief and Taunt are not)
-Cannot have items used on her other than Berries, and cannot hold items other than Berries
-Must solo all Pokemon that have Megas in the E4 that are not already taken by another solo.
-Against Steven's Metagross, must defeat both it and itself with Perish Song. Perish Song is the one exception to the no-status-moves rule.
-If possible, when the Scramble is completed, transfer Angel up to a 6th generation game to Mega Evolve her and complete her journey.
If it's too easy or too hard, I can tweak the restrictions.