Here is the full list of all 20 Astral Heroes achievements.
Defeat an opponent by dealing more than 20 damage with your final hit.
Win 10 matches in the League
Join an existing guild, or create a new guild
Successfully defend your guild caravan from the attack of another player
Successfully rob 3 caravans
Win a Draft Tournament in the Online League
Defeat an opponent using the attack of a Sheep as your final hit
Kill 100 vampires
Summon 100 elves
Complete 5 quests
Defeat a Quest opponent with 50 or more life remaining
Complete a Quest using a deck that contains no Spells
Complete a Quest using a deck that contains no Creatures
Defeat a Quest opponent after summoning 3 Dragons during the battle
Defeat a Quest opponent with 6 ally creatures on the board at the end of the battle
Defeat a Quest opponent with no ally creatures on the board at the end of the battle.
Collect 100 cards
Collect 200 cards
Collect 300 cards
Collect 400 cards