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