@Shrang: Chansey, Quagsire and Ferrothorn can take 2 LO EQs from Mamoswine. About the rotom suggestion, it might work (especially with wish support), but some set uppers like Dnite or Toxi would be too problematic. Mamo is a problem for most non Bronzong/Skarm rain stalls though.
@HBK: Tenta will beat CBtar unless it gets unlucky (it will get burned, and tenta has several attempts before dying). Just protect. If it pursuits, then Scald, if not, go to a counter. As I said, CBkion is an annoying pokemon that requires prediction, or it will beat you), and thats true for most stalls (gliscor has a 12.5% chance of being OHKOed by a CB SE with rocks!). With scarf rotom I could revenge kill it, but then Im weak to other common threats, and terrakion could just switch out and I would lose my main rock resist. I'm strongly considering Sr bliss and leech + protect ferrothorn, so I can deal better with Mamo, I can protect vs CBkion, so it would only be a problem if it switches into Chans, and it wont like a ST (especially if there are TS). The problem is that I would lose Wish (or Toxic), and both are quite important attacks for Chans
@Milanor: Ferrothorn is actually easy to beat. Chances are that Tentacruel wilp burn Ferrothorn (50%+ chance with 2 scalds, and I can use Ferrothorn in a predicted PW for a -25%. Ferrothorn will be burned most of the times by Scald, and a birned Ferrothorn will never beat Tentacruel.
About the skarm suggestion, I already explained the Ferro vs Skarm in the OP. I have some variants of this team with skarm though.