Empowered Spiritualist

This can be done in Normal Mode.
Just wait until three Empowered Zombies spawn, Cheers :)

Very simple at 120.

1. Facepull boss.
2. Wait until he does "summon empowered spirit" three times.
3. Double check that you have at least three empowered zombies hitting on you (more is fine, less is no)
4. Ignore their foul flirts and one-shot boss.
5. Enjoy mocking their corpses with your new achieve.

Don't worry about dpsing the boss, or cc'ing the zombies. No phases involved, and no damage can get through the 30 level gap.
If you have any auto-damaging armor, you may want to remove it.

You can get this achievement in the bossfight of Thalnos the Soulrender, the first boss of the Scarlet Cathedral.

The keypoint to get this achievement is in Thalnos ability "Summon empowered spirit". It will (of course) summon an empowered spirit who tries to reach the closest corpse of a crusader. Normally your group would try to kill it but if you want to get this achievement simply ignore the spirit. When the spirit reaches the corpse he will possess the body and will arise him as an empowered zombie - the objectives of this achievement. These zombies have much health (and are nearly unkillable because of that) and deal a lot of meleedamage to your tank. You have to wait until there are three of them, then finish the boss to obtain the achievement.

First of all, try to lower the health of Thalnos to something between 5% and 10%. Wait until there are enough empowered zombies up, then try to kill the boss as fast as possible.
The main problem is that your tank will have to tank the boss and at least three heavy mobs at the same time. The incoming damage will be very high, so your healer has to heal your tank as much as possible. The circumstance that the boss summons additional undead to help him doesn't make this easier, so you have to deal with the empowered zombies somehow.

Luckily, they ARE affected by stuns, slows and cc on the current beta build. That means you can use all abilities who can keep undead in cc like shackle from a priest or the "fear undead" ability by paladins. Please note that the most common cc won't work (like fear from a warlock or the sheep of mages - icetrap does, by the way). So if you have enough cc to keep them out of the fight this achievement won't be a problem. Of course no one should damage the empowered zombie because the cc will most likely break.

A very easy method to get this achievement is by simply having a second tank in your group who tanks two or three empowered zombies at the same time. This will lower your group dps but will prevent you from dying by the meleeattacks of the zombies. Please keep in mind that the healer will have to take care of two tanks at the same time, so use every available cooldown to lower the incoming damage.

Another way to get this achievement is to have a range dd kite the empowered zombies (preferably a frost mage). This is not recommended because a) you have to clear the whole graveyard and b) if an empowered spirit spawns while the kiter is far away from it he won't be able to pick them up at time which will most probably cause a wipe. You should only try this if you have no other options to take care of the zombies.

Have fun out there - good luck.