Well, looking at the calcs and all, it seems like a SmashPassed Zangoose is going to murder everything without priority (and if we give it Quick Attack it will demolish Breloom too, not sure about +2 Quick Attack on Mamoswine. It'd hurt for sure though). My vote goes towards a SmashPasser for it. Which one, I dunno XD
"Whether Castform the Weather Pokemon can weather the weather is dependent on whether the weather that it's weathering is the proper weather for it to weather. Whether the opponent can weather the weather is also subject to whether the weather that it's weathering is the right weather to weather. Whether Castform can weather the opponent is once again dictated by the weather and whether that weather is the favorable weather for weathering. But most importantly, you should know whether there will be weather to weather rather than what weather they will be weathering and whether they can weather that weather."
- Smogon's Castform analysis