Flaming Sword
From The Battle for Wesnoth Wiki
Flaming Sword is a sword driven into the trunk of a large tree in Snow Plains in Heir to the Throne.
Only the leader of an army (Konrad, Li'sar, Kalenz, Paladin, Elvish Marshal, Elvish Champion, Elvish Captain, Elvish Hero) can wield this sword.
As of version 1.16.9, it increases the wielder's sword damage by 25%, gives the magical weapon special, and changes the damage type from blade to fire. The wielder's other weapons are unaffected.
Before version 1.11.8, it used to change the sword damage to 15×4 for any wielder instead of the current 25% increase.