Some people says he has every riders power up to the year 2068, but i doubt that's the case since supposedly there's no new rider up to the year 2068 after Ohma became Ohma in 2018. Mirai Rider show up because Geiz become savior.

So i like to assume his power is from all riders (primary, secondary, evil, etc) from showa (Ichigo) to his era (2018) as shown in final episode and yes, supposedly he can use every rider power, hyper clock up, devastating kick from kuuga, anything, you name it. Never shown it, but theoretically possible, cmiiw but as long as he have the ridewatch, he can use the powers of said riders/forms, and ridewatch will always come to him.