There are hundreds of items to be discovered in Elden Ring: Shadow of the Erdtree DLC. This is a list of the most critical key items required in order to progress through the game.
Black Syrup
Speak with Moore till dialogue’s end near Belurat, Tower Settlement and collect the Black Syrup.
Deliver it to Thiollier.
Cross Map
Speak with Hornsent till dialogue’s end near Three-Path Cross and collect the Cross Map.
Reveals the location of three golden crosses.
Gaol Lower Level Key
Find it in the lower level of the Lamenter’s Gaol.
Opens the iron door on the lower level.
Gaol Upper Level Key
Find it in Lamenter’s Gaol within a chest.
Opens the iron door on the upper level.
Heart of Bayle
Defeat Bayle the Dread.
Use to trade for either Bayle’s Flame Lightning or Bayle’s Tyranny incantations at the Grand Altar of Dragon Communion.
Hole-Laden Necklace
Speak with Count Ymir at Cathedral of Manus Metyr the first time.
Use to acquire Cerulian Seed Talisman +1 at the Finger Ruins of Dheo.
Use to acquire Crimson Seed Talisman +1 at the Finger Ruins of Rhia.
Igon’s Furled Finger
Defeat the Jagged Peak Drake and speak with Igon.
Use to summon Drake Warrior Igon, when in Bayle the Dread’s arena.
Map: Abyss
Unlock the Abyss map fragment.
Map: Gravesite Plain
Unlock the Gravesite Plain map fragment.
Map: Rauh Ruins
Unlock the Rauh Ruins map fragment.
Map: Scadu Altus
Unlock the Scadu map fragment.
Map: Southern Shore
Unlock the Southern Shore map fragment.
Messmer’s Kindling
Defeat Messmer the Impaler. Use to burn away the tree obstruction in Belurat, Tower Settlement.
New Cross Map
Speak with Hornsent at the Sight of Grace in Highroad Cross.
Reveals the location of more golden crosses.
Prayer Room Key
Defeat Invader Fire Knight Queelign to acquire this key.
Opens the prayer room in the Church District.
Ruins Map
Speak with Count Ymir at the Cathedral of Manus Metyr.
Locates a Hallowed Ruin.
Ruins Map (2nd)
Speak with Count Ymir at the Cathedral of Manus Metyr.
Locates a Hallowed Ruin.
Ruins Map (3rd)
Speak with Count Ymir at the Cathedral of Manus Metyr.
Locates a Hallowed Ruin.
Storeroom Key
Pillage a corpse in Belurat, Tower Settlement to acquire this key.
Opens the storeroom door in Belurat, Tower Settlement.
Well Depths Key
Pillage a corpse in Belurat, Tower Settlement to acquire this key.
Opens the iron door at the bottom of the well in Belurat, Tower Settlement.
Those are all the major items in Elden Ring: Shadow of the Erdtree.