As I'm sure others have already told you. Serperior only really excels in speed. So either keep what you have and start breeding, or reset until you get a Timid-natured one to jump-start your breeding (unless you already have a flawless Timid Ditto...). No one here really cares about flawed events, even if they are special/in a Cherish ball - I'm sure there are dozens of casual sites out there where'd a decent SR'd Serperior would be worth something, just not here.
Honestly, don't bother resetting any breedables. If NO IVs or nature are guaranteed, then you are just wasting your time. Cos-chu, Story Lati@s, Mystery Gift Legendaries, and in-game Legendaries: YES; Mystery Gift breedables: NO.