I'm pretty sure that Tobirama kidnapped and experimented on countless Uchiha. He most likely had some human centipede-type shit going on that would put even Orochimaru to shame.
It's said that Tobirama stopped just short of completely destroying Madara's dead body, so he could've gained that knowledge from Madara's body. I do expect him to be the kind of guy to do the same to other Uchiha too though.
Who knows what he did. What we do know is that most of his work involved surgical procedures (to study the inner-workings of the Uchiha), deceased corpses (to invent Edo Tensei), hypotheses trials (to deduce his conclusion concerning the functionality of the Sharingan), manipulation of space and time (to invent Hiraishin), and a lot of other stuff I'm sure, that he most likely never got to finish or bring into fruition due to his early death. Orochimaru stole the formula for Edo Tensei from Tobirama (or recreated it, whatever), so I wouldn't be surprised if he also stole the organ-implanting methods (Danzo's arm, Shin's head) from Tobirama. Tobirama invented a lot of crazy things that would require some very weird procedures to create---and Orochimaru was no better. They probably had a bunch of cronenbergs limping around in whatever godforsaken laboratories they owned.
Who knows what he did. What we do know is that most of his work involved surgical procedures (to study the inner-workings of the Uchiha), deceased corpses (to invent Edo Tensei), hypotheses trials (to deduce his conclusion concerning the functionality of the Sharingan), manipulation of space and time (to invent Hiraishin), and a lot of other stuff I'm sure, that he most likely never got to finish or bring into fruition due to his early death. Orochimaru stole the formula for Edo Tensei from Tobirama (or recreated it, whatever), so I wouldn't be surprised if he also stole the organ-implanting methods (Danzo's arm, Shin's head) from Tobirama. Tobirama invented a lot of crazy things that would require some very weird procedures to create---and Orochimaru was no better. They probably had a bunch of cronenbergs limping around in whatever godforsaken laboratories they owned.
Orochimaru did say Tobirama was the one he admires the most there's a hint right there. Anyway his jutsu and knowledge definitely require experimentation the same as Orochimaru's did.