Appearently when you used the death eye while in the covenant you place a mark on the ground and 3 random worlds are chosen, these 3 chosen worlds will get invaded with enemy mobs that are harder to kill making progress harder then normal and the only way to stop this is by either getting killed or finding where the mark was put and invading the gravelords world and killing him.
From what ive gathered from various other forums most invasions are level specific which means you cant invade someone who is far lower level then you or higher. whether or not they enemy player has to be in human for for the Gravelord death eye to work is beyond me. But with the soul farming glitch people's levels are too widely apart for this covenant to work properly, that and there is in incentive to be alive. You're almost always going to die going into new areas and humanity is not an easy thing to find. So this covenant is pretty flawed right now. I've places the mark in multiple locations and waited hours with no random gains of souls or invasion to stop the death eye effect.