Here's my Volc team, I started with BulkyVolc as there are a lot of Mawile that are rly annoying to deal with & it check plenty of others mons if needed, next I added Gastrodon as a way to deal with Ash-Greninja which is a big threat to Volcarona due to Water Shuriken, and Gastrodon works really well here as a blanket special check, plus it let the opportunity to Volcarona to come in against opposing Grass-type that likes to threaten Gastrodon, next adding a Hazard Remover was a necessity, and I wanted something that could help me to alleviate Volcarona's job as it already is really important to deal with Mawile, I wanted another grass type answer and something that could add some kind of speed control, so naturally Tornadus-therian was immediatly my choice, next I noticed that I had troubles dealing with defensive core, especially those featuring the Pex, I also wanted a back up answer to Heatran as a potential Grassium Z Toxic could just defeat every member of the team at this point, thats how Gliscor came here, Ice Fang is very important here as Zygarde is a big threat to the team at this point. Ferrothorn came next as Volcarona
needs rocks up to do its job, I choose Ferrothorn because I know that i'll be forced to Defog at one point so I needed something that could SR multiple time, and with Volcarona attracting Water-Type, Ferrothorn has plenty of opportunity to set them up, plus Knock Off Ferrothorn is probably the easiest way to remove Heatran's leftovers which allows Volcarona to win the 1v1 if it doesn't have Toxic. Last but not least here's Diancie-Mega, I've wanted to use it in SM for so long, its a really potent Mega paired with Volcarona as with Magic Bounce you continuously pressure the opponent's rocker even without being on the field, I choose this set as a way to deal with Landorus-Therian as Protect let you scout the Scarf, HP Ice was initially here as an emergency button against Gliscor as it is a huge threat to the team, but it ended up being really useful as you have the opportunity to remove a non-scarfed Landorus really early as people tends to lead with it really often, and a Landorus dead is always sweet for a Volcarona team especially mine as it has multiple occasion to setup its rocks. overall its a really fun team that rely on Tornadus-Therian and Ferrothorn's Knock Off to create hole with Diancie/Gliscor to allow Volcarona to clean up later.