Here is the full list of all 20 Elements: Epic Heroes achievements worth 200 gamerscore.
Finish all the Forest's missions.
Kill 200 enemies.
Kill one Boss.
Finish the tutorial.
Upgrade all skills to level 4.
Clean the Desert Dungeon from enemies.
Get to the 5th floor in the Infinity Tower.
Kill the withe bear.
Clean the Swamp Dungeon from enemies.
Get to the 10th floor in the Infinity Tower.
Collect 1000 Dragon teeth.
Kill 2000 enemies.
Finish all the Desert's missions.
Kill 10 Bosses.
Finish all the Swamp's missions.
Kill the Nazgulz.
Finish all the Winter's missions.
Kill 100 Bosses.
Kill the Dragon.
Obtain legendary stuff.