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