it doesn't have to go to BL prior to going to OU, which is he case of Umbreon.
If it was used (not TOO sure of exact numbers) at least once out of every 20 games for about 3 months (?), it wil be OU.
As for Missy...I was thinking about using it as well but whih set do you think is the most effective? Ovrall ofc lol