I seldom see a Substitute Volcarona, if any. In my opinion, Substitute could work great on Volcarona as a buffer against pokemon trying to kill it, and also gives him the ability to quiver dance. However, Sub Volcarona does face many problems, being walled by Heatran, Dragonite, Salamence and friends completely. Despite this, I think with the right amount of support, Sub-Volcarona can still find its place to shine.