Here is the full list of all 44 Viking Brothers 6 achievements.
For defeating Nanook
For stopping the avalanche
For calling Ratatoskr
For saving the fishermen stranded on ice floats
For making 50 trades with the merchants
For accessing five walnut groves
For saving Yggdrasil
For preparing the truth potion
For accessing five taverns
For exposing Gullveig
For visiting the Spring of Urd
For visiting the Spring of Wisdom
For gathering 1,000 units of mana
For completing 30 levels with 3 stars
For visiting Hvergelmir
For breaking the wall of ice
For meeting Hraesvelg
For gathering 1,000 units of wood
For collecting 1,000 units of gold
For collecting 1,000 units of stone
For using a booster 100 times
For making magical wings
For canceling 30 tasks
For encountering an enemy patrol 30 times
For completing a level without using boosters
For meeting Volund
For gathering 1,000 units of food
For helping the Goddess Nott
For accessing a walnut grove
For reaching Yggdrasil
For completing 10 levels with 3 stars
For canceling a task
For encountering an enemy patrol
For gathering 100 units of mana
For making sleds
For gathering 100 units of wood
For accessing a tavern
For collecting 100 units of stone
For collecting 100 units of gold
For building an igloo
For gathering 100 units of food
For using a booster
For completing a level with 3 stars
For assigning five tasks at once