I disagree with Crawdaunt, lots of things outspeed it even after a Dragon Dance, and personally I have never had trouble with them (although I do use Gastrodon, who is the perfect counter for it, so I am a little biased...)Here are some threats that might be good to add:
Offensive Threats:
Crawdaunt. It gets Dragon Dance, adaptability and dual stab that is only resisted by one type (It gets super power for that though). It's a bit hard to pull of a dragon dance or two without a focus sash though.
Medicham. This thing requires quite a bit of prediction since the best sets are if it has a choice band or a choice scarf. It can at least 2KO nearly the entire tier using either Hi-Jump kick, Zen Headbutt, or Ice Punch if it has a Choice Band. With a choice scarf of course it'll be faster but it'll miss out on quite a few 2KO's or OHKO's.
Defensive Threats:
Poliwrath. While this pokemon doesn't have the best defenses it has a pretty good typing that allows it to survive an attack from most shell smashers and phaze them with circle throw and it also resists bug type attacks. (Although most bug types carry electric or grass type moves) It's also a pretty good counter for Durant since it resists it's common attacks and again can phaze it.
These are just suggestions though.
Medicham I agree with
Poliwrath is good, but it's not amazing. Once you know the set its running, its not that hard to get around. More of a minor threat than a major one.
Hydration is pretty useless on it though. The only status it ever gets is para, but most people go for the flat-out kill than trying to cripple it.He pairs pretty well with Rain teams, in my opinion. Fast Rain Dance, has Hydration, has Spikes and Yawn for support, all sorts of fun stuff to play with. I'm surprised more people don't use him.