This might be common knowledge to the people who did this quest already, but nonetheless I'm posting it to let everyone know .
So you're at the last part of your Destiny Quest level 80 (Defeat the Grim Grey God, objective), you might or might not have a hard time killing the waves of mobs, well here's a trick. All the tombs that gives you buffs, stack, so everytime you've went up and clicked one of the totems, you can get another pair of buffs, I ended up having 254% piercing, slashing and crushing resistance, which basically means you get life when hit by that type of damage. This makes the quest that much easier.
Hope somebody found this useful, enjoy!