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