Here is the full list of all 50 Eldest Souls achievements.
Reach the Crossroads
Defeat the Guardian.
Have at least 10 Windleaves active at once.
Hit an enemy with Windslide, Berserker Slash, or Counter 20 times.
Hit enemies with a thrust attack 200 times
Retry a Boss 10 times in a row.
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
Defeat the Watchdog while taking 0 damage.
Defeat the Guardian while taking 0 damage.
Defeat Azikel, God of Light.
Defeat Azikel, God of Light while taking 0 damage.
Defeat Eos, God of Unity
Defeat Eos, God of Unity while taking 0 damage.
Defeat Hyem of the Frigid Waste.
Defeat Hyem while taking 0 damage.
Defeat The Deer God and the Warden of Purity.
Defeat The Deer God and the Warden of Purity while taking 0 damage.
Defeat Aryana, First of the Moon.
Defeat Aryana, First of the Moon while taking 0 damage.
Defeat Drakmur, the Nightmare
Defeat Drakmur, the Nightmare while taking 0 damage
Defeat Eksyll
Perform 3 Perfect Counters in a row against any Boss.
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
Deliver the bag of crowns to Edelon.
Obtain the Empty Vessel
Gain the Blessed Feather of Dawn
Gain the Kindled Heart of Fire
Gain the Blessed Trueice Prism
Gain the Blessed Hunter's Charm
Gain the Abyssal Eye
Reach Concord Sanctuary
Reach the Steps of Ascension
Defeat the Guardian in Abyss Mode.
Defeat Azikel in Abyss Mode.
Defeat Eos in Abyss Mode.
Defeat Hyem in Abyss Mode.
Defeat The Deer God in Abyss Mode.
Defeat The Warden of Purity in Abyss Mode.
Defeat Drakmur in Abyss Mode.
Defeat Aryana in Abyss Mode.
Defeat Eksyll in Abyss Mode.