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