I find Bonemass much easier than Moder or The Elder. Flatten the ground around his statue. Attack with blunt. Always have poison resistance on. When health or stamina gets too low, just walk around the statue. That's all there is to it: walk around his altar in a circle. Bonemass follows at about the same speed, like in a slapstick movie. Kill his blobs on your way. When you have recovered enough (through time and potions), attack again. Rinse and repeat. Hard to lose that way, actually.