Here is the full list of all 9 Tidewoken Demo achievements.
Slay 10 monsters in any dungeon
Slay 35 monsters in any dungeon
Defeat Captain Dummy in the Training Chambers dungeon
Defeat Gniktar in the Treasure Room dungeon
Win your first PvP match in matchmaking
Win 10 matchmaking PvP matches
Complete the basic tutorial
Complete the advanced tutorial
Complete the Mystic tutorial