Here is the full list of all 35 Nekro achievements.
Kill 10 Mushroomheads.
Kill 50 basic Townies.
Use 10 different trinkets in one campaign.
Defeat Mayor Biscuit without dying.
Defeat the Citadel stage without dying.
Beat the campain with the Alchemist Powerset.
Kill 35 Witches.
Issue 50 orders to your summons.
Kill 35 Townie Elites.
Issue 10 orders to your summons.
Summon 30 Darkseeds.
Kill 50 Lumbros.
Pull 50 enemies with the Outcast's chain.
Kill 30 Pigs.
Kill 30 chickens.
Throw 50 healing vials.
Deploy 100 scourge.
Summon 30 Horrors.
Do any description of anything.
Beat the campaign without eating any animals.
Beat the campaign without taking any Nekro upgrades...you dirty boy.
Beat the campaign without using any Trinkets.
Beat the campaign without dying.
Find and befriend the Giant Flaming Bear.
Kill 35 Hunters.
Kill 35 Zealots.
Kill 35 Priests.
Issue 150 orders to your summons.
Issue 250 orders to your summons.
Issue 500 orders to your summons.
Beat the campaign with the Grimm Keeper Powerset.
Beat the campaign with the Outcast Powerset.
Smack 50 enemies with the Grimm Keeper's skull bag.
Summon 30 Punges.
Bestow the moniker of "Vance."