This was probably a typo, but Gardevoir has no place being in B rank. Gardevoir-Mega can be in B rank, but since we're ranking Mega Pokemon separate from their regular counterparts Gardevoir should probably be C or D rank.
Also, why is Thundurus-T C+ rank?? An insane 145 base SpA, 101 Spe, a solid ability, and multiple viable sets should put it in at least B or B+, maybe even A-. What page was Thundurus-T even discussed?
Finally, Crobat should be higher than C- rank. With blazing fast 130 Spe and Infiltrator, it can smack things behind subs with Brave Bird, or even status someone behind a sub with a 100% accurate Toxic. And it has a nice movepool consisting of Defog, Roost, Taunt, U-turn, and Super Fang, as well as the already mentioned Brave Bird and 100% accurate Toxic.
Overall, I'm nominating Gardevoir (regular) for C or D rank, Thundurus-T for B or B+, and Crobat for C+/B-.