Zygarde-10% C+ ---> B-
Even though Zygarde 10% is not as powerful attackwise as Zygarde 50%, it is very fast and can outspeed Latios, Keldeo, Terrakion, and Thundurus.
Buzzwole C+ ---> B
I know this is kind of a huge jump but Buzzwole has potential. A specific set I used made it very powerful...