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