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