Here is the full list of all 55 Bless Online achievements.
Entered a big city
Entered disputed territory
Participated in the Siege of Castra once
Achieved a set amount of points in the Siege of Castra
Faction was 1st place in the Siege of Castra
Dueled 3 times
Won a duel against a Guardian class character
Won a duel against a Berserker class character
Won a duel against a Ranger class character
Won a duel against a Mage class character
Won a duel against a Paladin class character
Visited the Arena once
9 kills in once match
Eliminated the opposing faction 3 times (Regardless of faction/content)
Killed someone ranked higher than a Commissioned Officer 100 times from the opposing faction (Regardless of area/content)
Completed the 2nd stage of Enemies and Monsters (1 species regardless of type)
Completed the 3rd stage of Enemies and Monsters (10 species regardless of type)
Completed the 3rd stage of Enemies and Monsters (150 species regardless of type)
Eliminated the Field Boss once
Reached +3 equipment enhancement level
Reached +10 equipment enhancement level
Reached max equipment enhancement level
First time gathering
Reached master level in gathering
Reached professional level in gathering
First time crafting
Reached master level in crafting
Reached professional level in crafting
Dismantled equipment 10 times
Dismantled legendary level equipment
One piece of your equipment's durability was at the red level
Cleared a dungeon(Urutus Mine) with all your equipment's durability level at orange
Repaired equipment durability using repair tools
Using repair tools recovered 1000 durability points (cumulative)
Joined a guild
Added a friend
Acquire 10 mounts/pets through taming
Acquire rare level mount/pet through leveling up
First time acquiring Activity points (Combat Points/Dungeon Point)
Used Activity points at the store (Combat Points/Dungeon Points)
Reached level 45
Used the market once
Entered the Gathering dungeon once
Acquired 20 items from the Gathering Dungeon
Acquired 100 hero level items from the Gathering Dungeon (cumulative)
Won a duel against an Assassin class character
Kill 10 general monsters in Basel Gorge
Won 5 times consecutively in the Arena
Cleared either the Underground Prison of Balmont or Guiscardo's Hideout 2 times
Cleared Kobold Hideout with a party
Eliminated the Roisa of Greed (Urutus Mine Troops)
Acquired high level crafting material from dismantling
All of your equipment's durability was at the red level
Cleared a dungeon with a friend in your party
Succeed in the Jackpot Mini-game 100 times