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