Why does tobi have sharingan in one eye and rinnagan in the other. i mean the rinnagan contains all the powers of the sharingan , MS , EMS and some powers of its own.
The only instance of the Rinnegan being able to do MS/EMS techniques is Madara. It's likely because Madara awakened the Rinnegan by further evolving his MS.
Tobi on the other hand stole the Rinnegan. Neither he nor Nagato progressed through the various stages of the Sharingan to reach it.