I've been reading a few threads on Tobiramas connection to possibly being tobi, or any involvment with Madara and I've put together My own thoughts as to Tobirama and his Edo Tensei.
Let's begin... here we see Madara admiting he has knowledge of breaking the edo contract and applying it to himself.
You must be registered for see links
So since Tobi did not know how to preform edo tensei, or how to undo it, Tobi is not tobirama (Tobirama's body with madaras soul in it theory is still on the table)
Moving on, So Madara knew of the Edo Tensei's flaw, how? Kabuto never told him, he merely summoned him then sent him off (I'm not going to get into a stupid argument that kabuto somehow told Madara how to void the contract...thats rediculous) So How did Madara learn of it? Oro? no, he was dead before Oro learned it.
So the only person living at the time of Madara with Edo tensei was Tobirama.
So now we ask the question "How?"
How did Madara learn of its flaw when only Tobirama was using it?
My theory is this, Tobirama did not label it a "forbidden jutsu because it was "evil" but because it's horrible flaw that could backfire on the user. So Tobirama banned it after it happened to him once, Madara learned of this by word of mouth since it was in fact a famous jutsu that got many kages attention and made Tobirama worthy of the title Kage, among other reasons.
So Madara learned how to break the Edo contract and fought Hashirama one last time to aquire his dna "Whether it was for the added chakra/"perks" or for the Rinnegan, knowing afterwards he would die.
He planned with Izuna for himself to be killed to be resurected via Edo Tensei with the rinnegan. Izuna would take his eyes back after Madaras death and become "tobi". Madara and Izuna both knew of nagato as a child and chose him to use the Rinnegan Since Madara had little time with it to "Learn of its abilities" So Izuna kept an eye on Nagato and gave his eyes to him during his "black out" and over time created akatsuki to Keep an even closer eye on nagato and learn all of the rinnegans abilities that Nagato unlocked. Izuna got another pair of eyes before have gave madaras to Nagato to continue functioning. (possibly Obitos, idk, i'm not concentrating on obito, just madara/izuna) Madara in Edo form would still have his eyes since he died with them intact.
The inbetween phase...
While Uchiha Madara is dead, Izuna has given madaras eyes to tobi and is continuing with his own plan to complete his brothers work (over throw konoha) while he waits for someone with edo tensei knowledge to appear. He learns of Oro and invites him into akatsuki for his ability of using the Edo Tensei.
You must be registered for see links
here we see kabuto being a spy for akatsuki but we all know after the "Kabuto backstory" chapters that he was a very good double agent, so he was working for Oro the whole time, Tobi knew this and let it continue knowing that Kabuto has the best chances of learning the Edo Tensei from him.
Fast forward, Tobi/Izuna has taken the eyes back from the deceased nagato. Kept 1 in his eye socket and the other in "storage" (We've all seen he has a vast storage of eyes before he transplanted itachis into sasuke) and knows that his brother is back as an eternal edo. And they can work together again both with rinnegan and all the biju as one immense Jubi. Tobi is not stupid, the infinite Tsumoyoki is not his real goal, his real goal is to be the elite duo of the past Madara and Izuna Uchiha WITH rinnegans both AND the jubi!
This is why Madara was playing with the kages, his real intent was to get the nine tails which he says here.
You must be registered for see links
Opinions?