Here is the full list of all 33 Niffelheim achievements.
Kill 1000 Skeletons
Kill 300 Skeletons
Kill 10 Buffalos
Trade for 10,000 Gold
Collect 10 Charms
Expose 10 Graves
Inflict 25,000 damage with a long-range weapon
Collect 100 Golden Ore
Survive for 200 days
Complete 10 Quests
Grow 200 Vegetables
Build all constructions of the highest level in a single Land
Kill 500 enemies with your Dragon
Reach Asgard at least once!
Reach Asgard in 100 days!
Kill 10 Bears
Consume 10000 HP
Survive for 100 days
Upgrade all Workshops to 9 lvl.
Build a lvl 1 stone Castle, Walls and Towers
Cook 100 dishes in the Kitchen Workshop
Activate the Dragon
Survive for 50 days
Use 20 different Potions
Craft 100 Alchemy items
Build a lvl 1 clay Castle, Walls and Towers
Eliminate 3 Bosses in underground caves
Activate 5 Charms
Kill 30 Spiders
Cut down 100 Trees
Complete 3 quests of the Priests
Craft 100 items in the Forge
Build a lvl 1 wooden Castle, Walls and Towers