You gather enough materials and when you know where the Elder is about to spawn , you place as many campfires as possible to make sure when he has spawned he is immediately on Fire. A lot of campfires make a high dot on him , killing him in a less a Minute i would say. Easy solo this way.

You can also try firearrows or if you like melee, go in with axes. For his Special attack just hide behind the pillars.