There's a utility item you can make after crafting something you get from defeating Yagluth. It's cheap and makes the Mistlands much easier to navigate. Otherwise devcommands and/or mods can remove or lessen fog for you.

RE: Ashlands lava I wouldn't be surprised if the Mistlands boss placeholder item (much like Yagluth had before Mistlands update) will likely be something that makes Ashlands much more doable.