A few tips to survive in elite nightmare mode
1. If possible, always pick armor gears with 3-5 level higher than your characters. If no suitable candidates, your must at least upgrade your armor gears 2 level above your character.
2. Again, pick the highest level weapons possible (5-6 level above your character). Higher level white/green weapons are more effective than a legendary weapons lower level than mobs, and cost points less too. I personally like weapons that does physical damage cause stunted enemies are unable to attack.
3. You must move your character ***very carefully***. Rush = death! Aggro few (1-2) mobs at a time, then move back to give yourself enough space to fight.
4. Put anti-shock or anti-stunt potions into your Q or E skill bar for easy access. My personally favorite is anti-shock.
5. If possible pick gears with high stunt defense strength.
6. Bring enough Health injectors.
7. Always kill vortexs first cause they always buff their fellow imps with purple shields.
8. When you get phased and overwhelmed by army of mobs, do not afraid to run away and pick them one by one. Knowing when to run away from a fight if just as important as knowing how to fight. I couldn't stress this point enough..
If you are able to follow all rules, you should be able to beat anything at least 5 levels above your character.