Here is the full list of all 21 Necromancer Returns achievements.
Complete campaign mode.
Summon 5 skeletons.
Learn all skills.
Upgrade all units.
Use units’ abilities 20 times.
Use Vampirism spell 5 times.
Heal 1000 of health.
Resurrect after death.
Complete all quests.
Win 40 battles.
Deal 5000 of magical damage.
Spend 10000 gold.
Put artifacts on the hero.
Win 20 battles.
Deal 15000 of physical damage.
Spend 200 of mana.
Deal 5000 of physical damage.
Lose 2000 of health.
Win in 5 battles.
Complete Tutorial.
Win in 5 battles in the mode of "Survival"