Itachi creating a big multi-step plan that involves making Sasuke fight him, getting pressured just enough to still believe it was a real fight, but also not get seriously hurt or killed, then getting pressured so that he'd rely on Orochimaru's power and release him, so that Itachi would seal him away and rid Sasuke of him, then manipulate Sasuke into awakening the Mangekyō through his death, and then awakening the EMS thanks to his eyes. He did all that while he had a failsafe in place to deal with "Madara's" interference through an implanted Amaterasu booby trap, and a plan to use Kotoamatsukami on Sasuke in case he went rogue through Naruto.
He put all that together while dying of a terminal illness, and covering his tracks from both the Akatsuki, Konoha, and Sasuke; all while giving an Oscar worthy performance to boot!
He also quickly figured out how to counter the Rinnegan against Nagato, something that Naruto couldn't pull even with prior knowledge. And he figured out how to stop the seemingly flawless Edo Tensei, almost singlehandedly ending the war.