Quote Originally Posted by Splash!
^^ No he didn't make all that up. Go reread Chapter 318. Someonemanr is right on the mark about both Tobi using a special jutsu on the 3 tail as well as what Deidrara said.
There's no indication of Tobi actually being the one to take it out. The only attack shown is one of Deidara's bombs in 317, then in 318 Tobi is standing on top of it declaring that it was nothing for him. Afterwards, Deidara states that Tobi would have had no chance if it weren't for his explosives. It seems to me like Deidara beat it up with some bombs and let Tobi get the final blow.