Originally posted by: BOARD_of_command
Oh well, 1 night. But still, that's a really short time to master a Jounin level technique.
He mastered it about the time it said in the anime that Kakshi knows all of Konoha's Jutsus. 1 night of focusing only on shadow replication(it is just an upper level of a technique that they showed you in the academy) and he learned how to do it, I don't see what is so impossible about it, he still sucks at it but he can do it...

some ppl say this jutsu is nothing necessary in fights.....................like just to teach naruto control his chakra and only can spin the enemy a little
I seriously doubt it personally but we won't know until later I suppose.