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