Mercurius

The Mercurius (translated as Mercury Sword in the Japanese versions) is a legandary sword that appears in Fire Emblem: Ankoku Ryū to Hikari no Tsurugi, Fire Emblem: Monshō no Nazo and Fire Emblem: Shadow Dragon. It was taken by the Grust forces, but retrieved by Est. In Monshō no Nazo, Astram wields Mercurius.

Ankoku Ryū to Hikari no Tsurugi
Weapon Type: Sword Weapon Level: N/A Mt: 18 Wt: 1 Hit: 100 Crit: 10 Range: 1 Uses: 24 Worth: N/A Effect: Marth only, increases growth rates.

Monshō no Nazo
Weapon Type: Sword Weapon Level: 12 Mt: 20 Wt: 4 Hit: 100 Crit: 0 Range: 1 Uses: 24 Worth: 24000 Effect: Doubles experience gain.

Shadow Dragon
Weapon Type: Sword Weapon Rank: A Mt: 18 Hit: 100 Crit: 10 Wt: 8 Range: 1 Uses: 20 Worth: N/A Weapon Exp: 2