1) Murkrow
2) Meditite
3) Silly Swagger Nonsense stuff
Murkrow is obvious. Because of its different sets, mainly LO Mixed, SubThief, and Swagplay, it has no true counters, and each set is viable in its own way. I was on the fence about Krow for a while, but the SubThief set helped make my decision.
I'm nominating Meditite on principle that he could become too strong or centralising if Murkrow is gone. He isn't the dominant force Murkrow is by any means, but he's one of the major reasons that this metagame is overly aggressive in the first place (obvious other reasons including Knock Off buff and Berry Juice being legal), and while that alone isn't a reason to ban him, the fact that he can tear through so much of the metagame with ease is ridiculous. His most reliable defensive checks, Honedge and Slowpoke, both have major weaknesses hindering their usage, and can both be beaten by Meditite carrying the proper move.