Awesome Anti-weather stall team, i love that <3
Confirm that Shed Shell on Skarm is a solid choice, then you can safely switch in Gastrodon/Roserade on the magne's t-bolt.
Another annoying pkmn that i faced testing this team is HP Grass/Flamethrower/earth Power/SR Heatran since takes care of your defensive core, but i play around gengar and Reuniclus predicting the right attack from heat and (CMing) focus blasting him (it's a lucky momentum, yeah) and is a very rare set.
Maybe LO on Gengar can be a good choice but needs testing.
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