Lots of fire arrows, drop a few campfires around the base for him to walk into for an extra boost of damage. Then just play chasie around pillars shooting at him. Using the pillars to shield yourself from the vine whips he shoots at you works well and dodging the roots that he brings up is easy. Takes a little time but it's easy. Build a spawn hut a little ways off. If you're daring or a playing with a friend, have them go in with an axe for max damage and drawing aggro while you shoot.