Spoiler: This was way back in beginning of get Gaara back arc and I'm still not sure what he means, is he talking about turning into kyubi with the tails? Cause that's not really a jutsu. And now he's suddenly learning a new jutsu, did Kishimoto forget about this? Or does this mean Naruto knows a forbidden jutsu that we might see later on? That would certainly be cool. I put spoiler tag in case you haven't been reading up.