Here is the full list of all 15 Might and Magic: Duel of Champions - there are Forgotten Wars achievements worth 400 gamerscore.
Reach Level 35
Win 10 ranked duels using a deck with no more than 1 copy of any card
Win 10 ranked duels playing no spells or fortunes
Over kill your opponent by at least 5 damage in a ranked duel
Cast Armageddon and have at least 1 surviving creature left on your side in a ranked duel
Own a copy of every card from the first Base Set
Win 30 Practice duels against your Friends
Reach Level 10
Win 3 Ranked duels in a row
Reach Level 2
Complete the Tutorial
Reach the Champion class
Destroy 250 creatures
Win 50 Ranked duels
Win 250 Ranked duels