Here is the current list of all items that can be upgraded with Soul Coins:
Weapons:
- Adamantine Longsword
- Adamantine Mace
- Adamantine Scimtar
- Ambusher
- Assassin's Touch
- Belm
- Bigboy's Chew Toy
- Blackguard's Sword
- Blade of Opressed Souls
- Blightbringer
- Blood-Bound Blade
- Blooded Greataxe
- Bow of Awareness
- Bow of the Banshee
- Cacophony
- Caitiff Staff
- Charge-Bound Warhammer
- Cold Snap
- Corpsegrinder*
- Corrosive Flail
- Crossbow of Arcane Force
- Cruel Sting
- Darkfire Shortbow
- Deep Delver
- Defender Flail
- Despair of Athkalta
- Dolor Amarus
- Doom Hammer
- Dragon's Grasp
- Drakethroat Glaive*
- Dread Iron Dagger
- Duke Ravengard's Longsword
- Dwarven Thrower
- Everburn Blade
- Exterminator's Axe
- Faithbreaker
- Firestoker
- Flail of Ages
- Fleshrender
- Foebreaker
- Gleamdance Dagger
- Gold Wyrmling Staff
- Halberd of Vigilance
- Hamarhraft
- Handmaiden's Mace
- Harmonic Dueller
- Harmonium Halberd
- Harold
- Hellbeard Halberd
- Hellfire Engine Crossbow
- Hellfire Greataxe
- Hellfire Hand Crossbow
- Hellrider Longbow*
- Hollow's Staff
- Hunter's Dagger
- Intransigent Warhammer
- Jorgoral's Greatsword
- Ketheric's Warhammer
- Knife of the Undermountain King
- Kurwin's Cauterizer*
- Larethian's Wrath
- Least Expected*
- Light of Creation*
- Loviatar's Scourge
- Melf's First Staff
- Monster Slayer Glaive
- Moonlight Glaive*
- Mourning Frost
- Ne'er Misser
- Pelorsun Blade
- Phalar Aluve
- Ravengard's Scourger*
- Render of Mind and Body
- Returning Pike*
- Sethan
- Shortsword of First Blood
- Slicing Shortsword
- Sorrow
- Soulbreaker Greatsword
- Speedy Reply
- Spellthief
- Staff of Spell Power
- Staff of the Emperor
- Stillmaker
- Sussur Dagger
- Sussur Greatsword
- Sussur Sickle
- Svartlebee's Woundseeker*
- Sword of Clutching Umbra
- Sword of Justice*
- Sword of Screams
- Sword of the Emperor*
- Sylvan Scimtar*
- The Baneful
- The Dancing Breeze
- The Dead Shot
- The Joltshooter*
- The Skinburster*
- The Sparky Points*
- The Spellsparkler*
- The Watcher's Guide
- Thermodynamo Axe
- Titanstring Bow
- Trident of the Waves
- Twist of Fortune
- Unseen Danger
- Vicious Battleaxe
- Vicious Shortbow
- Vicious Shortsword
- Vision of the Absolute
- Wavemother's Sickle*
- Witchbreaker*
- Xyanyde*
* = Item has had its base rarity adjusted