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