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