Adds 5 bonus fire damage to the attack of a Hero when carried. The Hero's attacks also become ranged when attacking air and do splash damage to nearby enemy units.
These can be bought from Arcane Vaults in Frozen Throne.
Arthas receives one in Blackrock & Roll, chapter 2 of the Warcraft III human campaign, The Scourge of Lordaeron, after delivering The Heart of Searinox to Feranor Steeltoe.
Grom Hellscream finds one in The Hunter of Shadows, chapter 5 of the orc campaign, The Invasion of Kalimdor.
Thrall finds one in The Oracle, chapter 7 of that campaign.
Tyrande and Maiev can find one in Shards of the Alliance, chapter 6 of the Frozen Throne sentinels campaign, Terror of the Tides.
In Reign of Chaos the tooltip said: Adds 5 bonus fire damage to the attacks of a Hero when carried. The Hero's attacks also do splash damage to nearby enemy units.
In an earlier version of Warcraft III: Reign of Chaos, it gave you 12 bonus fire damage.