I just ran an adult Volcanic Dragon this past week against my party (along with an adult Battle Dragon and adult Blight Dragon in the same encounter). The volcanic dragon's biggest concern should be using all of his powers, as often as he can. He should be powering his aura every turn; using a standard action to bring it to bear initially is worth it. He should drop lava as often as he can - in fact, dropping it nearly on top of himself to help deal a little extra damage against opponents in melee helps a great deal. And this goes without saying, but claw those with fire resistance. All in all, a really fun creature to use.