In order to add these wings to your collection, you have to complete ALL Necromancer achievements.
The Silence When You Speak to Me
Go to the 8th quest of Act 5 in campaign and listen to all of Master Ordan's conversations. More conversations will be unlocked as you move forward through the campaign. The last conversation is unlocked upon killing Malthael, so don't leave your game just yet. Teleport back to the waypoint in Pandemonium Fortress 1 when you kill him.
Serve the Balance
It can't be more self-explanatory than that. Reach level 70 with the Necromancer.
Bringer of Order
You only need to kill Malthael, so you could find someone who can do this for you instead of completing the whole act 5 yourself!
Use Bone spear with the Blighted Marrow or Teeth rune and go to the Fields of misery (or Cow level). Gather a big group of monster and cast the Bone Spear.
What Is Dead Can Sometimes Die
You can do this achievement in Normal difficulty with 2 piece bonus of the Pestilence Set in combination with Devour (devouring aura). This achievement can be combined with the Curse Your Enthusiasm and Skeleton Crew achievements.
Curse Your Enthusiasm
Just spam your Curse skill before killing the enemies.
Terror in the Blood
Use Death Nova with the Blood Nova rune. Go to Normal using just a weapon (take off the rest of your gear). Make sure you don't have thorns, life per hit or life per second, otherwise you will regain hp too fast. This achievement can be combined with Self Controlled.
Game of Bones
Cast Bone Armor to kill Leoric in Normal difficulty.
This achievement takes the longest to complete because on average you kill between 20-30 elites in a rift. Play on low difficulty (Normal or Torment 1 depending on your damage and how fast you want to complete the achievement) and always command your skeletons to attack the elites first before something else kills them
Your Simulacrum clone must kill the clone Diablo spawns. The Simulacrum clone casts the same skills whenever you do and you wamt only your Simulacrum clone to be in range. You may use Blood Rush to get away.
If you need guide for Necromancer sets look this post with All 4 set dungeons - locations , tasks and layouts