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