How do you use Poison type?

There's a lot of full or mixed Poison type mons with plenty of STAB attacks. Most of them seem to be in the right CP range for prestiging, but I never use them and I don't know what to do with them (I haven't evolved Muk yet).
Poison is best against Grass and Fairy. There's enough Fire types against Grass that Poison is not necessary here.
The only fairy gym defender is Blissey and although I haven't tried, I don't think an army of Arbok will kill it before timing out.

SO, do you use Poison types for any particular match-up?
Is Muk the only useful Poison? have you tried it against Blissey?