Hatred the Togepi
XAkaviri, take Hatred the Togepi. When Hatred was in its egg, a mishap occurred that caused it to be emotionally inverted, causing it to mercilessly attack whatever it comes across (can't switch out, always under the effect of Taunt. Metronome doesn't count as an attacking move) and also because of the mishap, Hatred despises everybody, but you in particular to the point where it will accept absolutely no items from you and will attack its teammates in double battles.
Now, you're probably thinking "How is Hatred supposed to evolve if Togepi's means of evolution is happiness?" The answer to that is it won't, unless of course it successfully soloes the Rocket Grunt in the Kimono Dance Theater (yes, that's what it's actually called) and later the Kimono Girls themselves. The reason for this is because the Kimono Girls are the ones who originally posessed the Togepi egg. After defeating them, Hatred must lead your party when you go to the Whirl Islands to battle Lugia. (Note: Hatred does not have to battle Lugia.) In case you're wondering why, the dance the Kimono Girls perform there is not only to awaken Lugia, but also as a purification ceremony, much like in Pokemon Colosseum and Pokemon XD's Agate Village. In other words, when the Kimono Girls are performing under Whirl Islands, they are essentially "purifying" Hatred, causing it to become a normal Togepi that loves everybody and everything, allowing it to evolve.
Now that Hatred has been purified, it decides to refute its own ways, meaning that every restriction it had as a Togepi is now reversed. (it will accept items from you, it can only have one attacking move which it cannot use unless it has used its other moves in the same battle, will never attack its teammates, is able to switch out) Also, Hatred decides to change its moveset entirely (Note: the amount of attacking moves Happiness can know is the opposite of how many it had as a Togepi. For example, if it had 3 attacking moves as a Togepi, it can only have one as a Togetic, and if it had 2 as a Togepi, it will have 2 as a Togetic.) and change its nickname to Happiness in commemoration of this. Finally, to prove that it loves you rather than hates you, it soloes an Elite Four member of your choice. After that is completed, Happiness may evolve again.
Have fun!
(^Perfect example of what I want^)
Joey the Rattata
You get Joey the Rattata. He must be a Male Rattata, and must be caught in Route 29 immediately after receiving your first Poke Balls. He is the 1% of all Rattata! In order to evolve him into Raticate, he must meet all of the following criteria:
Defeat Joey's Rattata in Route 30 at level 3.
Defeat Joey's Raticate in Route 30 (rematch battle) while level 29 or lower.
Must have the ability Run Away.
His moveset must include Quick Attack, one STAB that's not Quick Attack, one non-STAB, and one status move.
Furthermore, he must successfully employ the F.E.A.R. strategy against any Gym Leader before you are allowed to fight Red (since getting a Focus Sash is impractical, use Endure to accomplish this).
Leaf the Chikorita
XAkaviri, keep Leaf the Chikorita, except now it's only allowed moves of 35 BP or less (again, they can only be physical after the split) and this cap increases by 5 every badge. Again, must evolve into Bayleef after the third gym and into Meganium after the kimono girls.
Ash the Zubat
@XAkaviri you want a hard one? Okay, take Ash the Zubat. Ash “wants to be the very best, like no one ever was” (yes, you have to sing the song in your head). Ash must solo any other Zubat-lines as a Zubat. Ash must solo Whitney to evolve to Golbat, since he hears she is a very tough Gym leader to battle. Once Ash is a Golbat, he must defeat any pokemon he is sent out against, or die trying, along with soloing Zubat-lines. Ash must solo Jasmine to evolve to Crobat. Once Ash is a Crobat, he must never switch out against any pokemon (unless they have SE STAB), along with the other two challenges. Ash must solo Archer to prove he is the best Crobat/team member. Now that Ash thinks he is the best, he thinks he can take any pokemon you can throw at him. He must never switch out against any pokemon. He must also solo your rival in Victory Road. He must solo Will of the E4, and then is the best of the best. If you are going through to Red: He must solo Lt. Surge and Sabrina. He feels he is the strongest in the world now. He must solo Red’s Pikachu and any other ONE of Red’s pokemon.
All challenges:
As a Zubat:
- solo all other Zubat-lines
- solo Whitney to evolve
As a Golbat:
- defeat any pokemon switched into
- solo all other Zubat-lines
- solo Jasmine to evolve
As a Crobat:
- never switch out against un-SE pokemon
- defeat any pokemon switched into
- solo all other Zubat-lines
- solo Archer
As a (better?) Crobat:
- never switch out, period
- defeat any pokemon switched into
- solo all other Zubat-lines
- solo rival in Victory Road
- solo Will
If you are going through to Red:
- solo Lt. Surge
- solo Sabrina
- solo Red’s Pikachu and ONE other pokemon of Red’s
I HOPE YOU SUFFER GL;HF! I hope it's hard enough for you...
CageMemory the Dratini
Take CageMemory the Dratini.
One day, a Dratini was slithering along in the Dragon's Den. Suddenly, a bunch of asshole poachers entered the den, grabbed this Dratini, and brought it off to the Goldenrod Game Corner, where it was to be a prize to those who spent enough time flipping Voltorbs the finger. Eventually, you enter the Game Corner and see its plight. So, you spend hours earning coins off the slave master (a.k.a. Mr. Game) by playing his torturous game, eventually clinching enough coins to buy this Dratini out! But it seems the countless days it spent in a cage in the game corner have had a few effects on it...
After all the months spent watching Voltorbs appear and prevent customers from freeing it, CageMemory has a perennial hatred for these abominations of nature. So, it must destroy every Voltorb or Electrode it comes across, no exceptions.
Being sold simply as an object for money has made it loathe money. It will not use any items that can be bought (even if you didn't actually buy them).
Mr. Game's face has left its imprint on its mind. So, it must solo all Gym Leaders with moustaches (i.e. Chuck and Blaine), as well as the Team Rocket Executive with the stupid-ass face, Petrel (on both occasions).
Good Luck; Have Fun!