Personally I think Mistcaller is a bit underwhelming. It's good in slower games, but a rather dead draw versus aggro. And it makes your fire elementals BGHable. Kappa.
I might have to experiment more, but I just don't like the spot it fills. There's too much other stuff you can put in like Dr. Boom, Harrison, Loatheb, etc. that's better tech. As a standalone bomb he's not very good, since he doesn't have much synergy with the totem archetype. Probably needs a more tailored deck to support him.
Seems better in midrange or control matchups though.