Soul Coins in Baldurs Gate 3 are rare and valuable items that contain the souls of the damned. They can be found in several locations throughout the game. At the moment, their only known use is to give Karlach, a companion character, a damage buff called Infernal Fury when she consumes one. This buff makes her melee attacks deal extra fire damage when she is low on HP or Raging. However, players should be careful with using Soul Coins, as they might have other uses later in the game. Here are some locations where you can find Soul Coins:

• Inside the Dank Crypt
• Directly south of The Risen Road waypoint
• Philgraves Mansion, close to the Heapside Strand waypoint, in the Lower City during Act 3
• Speak to Lann Tarv while Karlach is in your party in the main hall of the Moonrise Towers

If you dont have Karlach in your party, you wont have a reason to carry around Soul Coins.