Here is the full list of all 35 Nekro achievements.
Kill 50 Lumbros.
Issue 50 orders to your summons.
Issue 10 orders to your summons.
Kill 30 Pigs.
Do any description of anything.
Kill 30 chickens.
Beat the campaign without eating any animals.
Kill 10 Mushroomheads.
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 50 basic Townies.
Kill 35 Witches.
Kill 35 Hunters.
Kill 35 Zealots.
Kill 35 Priests.
Kill 35 Townie Elites.
Deploy 100 scourge.
Issue 150 orders to your summons.
Issue 250 orders to your summons.
Issue 500 orders to your summons.
Beat the campain with the Alchemist Powerset.
Beat the campaign with the Grimm Keeper Powerset.
Beat the campaign with the Outcast Powerset.
Throw 50 healing vials.
Pull 50 enemies with the Outcast's chain.
Smack 50 enemies with the Grimm Keeper's skull bag.
Summon 30 Horrors.
Summon 30 Darkseeds.
Summon 30 Punges.
Bestow the moniker of "Vance."