Here is the full list of all 50 Viking: Battle For Asgard achievements worth 1,000 gamerscore.
Collected all the skulls in Galcliff
Collected all the skulls in Niflberg
Completed Viking on the hard difficulty setting
Liberated Galcliff on hard difficulty level
Liberated Niflberg on hard difficulty level
Collected all the skulls in Isaholm
Completed Viking on the normal difficulty setting
Achieved the perfect victory at the final battle for all Midgard
Achieved victory at the final battle for all Midgard
Killed 5 Giants
Summoned the dragon-guardian of Isaholm
Isaholm farm, still, lumber mill, and quarry freed from the Legion
Unlocked all advanced combat moves
Achieved victory at the battle of Thornvik
Absolutely immolated a Legion
Blasted a Legion with Thor's ultimate lightning
Mastered the ultimate ice attack
Liberated Galcliff on normal difficulty level
Achieved victory at the battle of Caldberg
Killed Hel's Harbinger
Incinerated 10 Legion soldiers
Powered-up over 500 Vikings using the magic of the runes
Defeated a Legion Giant
Summoned the dragon-guardian of Galcliff
Galcliff farm, still, lumber mill, and quarry freed from the Legion
Killed 10 Champions
Demonstrated uncanny deadliness with throwing axes
Mastered 12 advanced combat moves
Mastered 8 advanced combat moves
Achieved victory at the battle of Holdenfort
Killed a Legion Champion without being hit
Executed 100 sneaky kills
Liberated Niflberg on normal difficulty level
Achieved victory at the battle for Darkwater
Summoned the dragon-guardian of Niflberg
Sneaked into the infested settlement of Darkwater
Niflberg farm and quarry freed from the Legion
Performed 150 fatalities
Killed 500 Legion in Midgard
Defeated a Legion Assassin
Pushed 20 Legion off cliffs to their death
Defeated a Legion Champion
Performed 100 fatalities
Killed 200 Legion in Midgard
Killed 50 Legion without using a health potion
Killed 100 Legion
Unlocked 4 advanced combat moves
Mastered the first advanced combat move
Performed 25 fatalities
Killed 50 Legion in Midgard