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