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