I was reading earlier and saw something Pyro had said about 'updating' the game, and it gave me an Idea.
What if once you reach, say 50 Oro kills, You finally get rid of Oro, and from then on you fight Pein.
So my idea for fighting Pein is that it instead says Fight Pein or whatever, then each time you challenge him you fight one of the Random Realms of Pein.
Each Path of Pein as a different ability, so you don't know what your going against when you challenge him.
the Abilities could be as Followed.
-Deva Path (天道, Tendō)-
Shinra Tensei, the ability to repel or attract you. Every other turn it could randomly choose to repel, or attract.
-Attract will lower your Def to near Zero, as he would be drawing you in so you'd have little chance to defend.
-Repel would make him unable to be damaged for that round.
Like I said above he could only do one of these attack every other round due to the fact he can't use it in succession with out a short time gap between the uses.
Also this path makes Attacking and Defending harder.
-Human Path (人間道, Ningendō)-
Soul Removal, the ability to remove your soul, instantly killing you, however it takes time to do so.
-After like 2-3 round if you haven't killed this path, he would have had time to remove your soul, and instantly killing you.
The Soul Removal seems to take time to do, so that is why there is a time limit.
This path sets a time limit which you have to kill him within, making you need to strike quick and hard.
-Asura Path (修羅道, Shuradō)-
Kaiwan no Hiya, the ability to fire his arm like a rocket at you.
-Each round he would fire his arm, in an attack much like Snake arms with Oro.
-He also is shown to withstand great deals of Damage so his HP could be double or something.
His attack seems to be a powerful hit, and he has been shown to take huge amounts of Damage and still be able to fight.
This path is not only Tough, but also has a good attack which makes him even harder to defeat.
-The Animal Path (畜生道, Chikushōdō)-
Kuchiyose no Jutsu, summoning jutsu.
-Summons one of the random Rin'negan beasts each realm.
Each round this path can summon a Beast, much like Oro's Forbidden Clone Jutsu.
The path itself many not be strong, but it's Summons make it harder to beat.
-Preta Path (餓鬼道, Gakidō)-
Sealing Technique Absorption Seal, the ability to absorb your Jutsus.
-Makes the player enable to use Jutsu against this path.
-Also Removes any buffs before hand, except maybe racial buffs and KG eg. Sharingan, Current gate etc...
This path has shown the ability to nullify any Ninjutsu used against it.
This path will make you fight it with Raw power.
-Naraka Path (地獄道, Jigokudō)-
King of Hell Genjutsu.
-Uses his Mystery Genjustu on you to greatly reduce your atk and def.
Not much know about this Genjutsu, besides the fact it is used for interrogation.
this path makes you fight with much lower stats then Normal.
Now I know some people might not like this idea, but it makes kill Oro/Pein hard, and a bit more of a challenge.
Also it stops people getting Flawless Oro kills every time, as there will be no one way to kill him easily, due to the random fact.
And after a while people would learn each paths weaknesses anyway.
Let me know what you think, this is just an idea anyway.