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