Axe is pretty good against the Elder for obvious reasons. It might take a bit longer to kill him in melee as opposed to using fire arrows from behind the pillars. The 2 handed Atgier special attack might also be good though I haven't tried that.

Perhaps if the vertical hit box isn't that high you could build platforms attached to the pillars and then melee him with the axe in relative safety as he stomps on the ground or summons his vines. This is how I deal with a certain large enemy from the Swamp biome. If he does continue to use his ranged attack this tactic wouldn't work.