If we were judging this by my playthrough, I'd put bibarel in at least the B tier.
Don't worry, i'm not screwing around, here's why.
Up to level fifty before i caught Gengar, Bibarel (you can quote me on this) Steamrolled everything with moody. It requires way too much luck, but what i would do is (if against a special attacker) use amnesia or headbutt (if against a physical one) and hope for a flinch. After around 4-5 turns, if bibarel lives to that legnth, he's done, and you can roll over anything.
I think it should be higher, but thats because i'm a sucker for gimmicky pokemon.