Here is the full list of all 50 Eldest Souls achievements.
Defeat the Watchdog while taking 0 damage.
Defeat Eksyll in Abyss Mode.
Defeat Aryana, First of the Moon while taking 0 damage.
Defeat Aryana in Abyss Mode.
Defeat Drakmur, the Nightmare while taking 0 damage
Defeat Drakmur in Abyss Mode.
Defeat The Deer God and the Warden of Purity while taking 0 damage.
Defeat The Warden of Purity in Abyss Mode.
Defeat The Deer God in Abyss Mode.
Gain the Kindled Heart of Fire
Defeat Hyem while taking 0 damage.
Defeat Hyem in Abyss Mode.
Defeat Eos in Abyss Mode.
Defeat Azikel, God of Light while taking 0 damage.
Defeat Azikel in Abyss Mode.
Defeat the Guardian while taking 0 damage.
Defeat the Guardian in Abyss Mode.
Defeat Eksyll
Reach the Steps of Ascension
Defeat Drakmur, the Nightmare
Gain the Abyssal Eye
Obtain the Empty Vessel
Perform 3 Perfect Counters in a row against any Boss.
Hit enemies with a thrust attack 200 times
Gain the Blessed Feather of Dawn
Defeat Aryana, First of the Moon.
Hit enemies with a Shard attack 200 times
Deliver the bag of crowns to Edelon.
Die to a rolling log.
Defeat The Deer God and the Warden of Purity.
Defeat Hyem of the Frigid Waste.
Hit an enemy with Windslide, Berserker Slash, or Counter 20 times.
Reach Concord Sanctuary
Defeat Eos, God of Unity
Retry a Boss 10 times in a row.
Defeat Azikel, God of Light.
Deliver the harp string to Edd
Reach the Crossroads
Defeat the Guardian.
Have at least 10 Windleaves active at once.
Die to a Boss.
Talk with Rass
Defeat the Watchdog.
Reach Crusader's Landing
Defeat Eos, God of Unity while taking 0 damage.
Maintain 4 stacks of Berserker for 30s.
Reach the ending without dying once.
Finish the game without activating any Shard or Infusions.
Gain the Blessed Trueice Prism
Gain the Blessed Hunter's Charm