Found among the rats in the barn, reached from the roof of the fort.
From the entrance, climb up the ladder and drop down from the tower onto the fort's roof. Drop down the hole on the other side of the gallows and go left and forwards of the ladder, then jump across to a second walkway. Drop down the ladder at the end and reach the end of this small section to find the Talisman.
Radagon's Soreseal fares best on lower level builds, but can become a bit of a trap if worn too long. In the early game, the stat increases more than make up for the extra damage taken in practice due to the high returns of HP at lower levels of Vigor, the significant bump in flat Defense from effectively being 20 levels higher, and the increased Equipment Load allowing players to wear heavier armor sooner. The increased Strength and Dexterity also have greater utility early on, when players have fewer points to spare to meet weapon requirements. However, as the player levels up their stats, they will eventually reach a point of diminishing returns, where +5 to a given stat simply doesn't provide as large an impact proportionally. Meanwhile, -15% Damage Negation only becomes an increasingly dire debuff as the player gets further into the game and enemies hit for larger and larger amounts of damage.
Once the player hits Vigor's first softcap of 40, it's better to remove the Soreseal and replace it with another talisman that provides either a percentage increase to the associated attributes or a flat stat increase without lowering Damage Negation. For example, more HP can be obtained from the Crimson Amber Medallions, more Equipment Load from the Arsenal Charms, and more Strength or Dexterity from their associated Heirlooms.
Considered a variant of Radagon's Scarseal, the two cannot be equipped at the same time.
This is one of the eight talismans needed for the Legendary Talismans trophy/achievement.