stand in front of a pillar on ground, dodge attacks, when underground, get on stone floor infront of pillar , push the pillar on to demon, repeat 3 times

Stand on the ground near one of the four pillars, avoid shock waves and fire balls.When the Earth Demon goes underground he'll head your way. Get behind the pillar as the demon comes up he will hit his shead on the side and get knocked out for a while. As is lying on his back push the pillar onto him. You,ll need to do this three times to defeat him.