Runehammer

Runehammer +4 is an enchanted hammer, which inflicts 2d4 +4 points of damage and 4-16 +8 points of damage against undead creatures, plus they must make saving throw vs. with a -4 penalty or be destroyed instantly. The weapon also provides the wielder protection from energy from the negative plane, which makes them immune to level drain.

The hammer gives the wielder a -4 THACo bonus, the weapon itself weighs only 3 lbs and it has a speed factor of 0. The wielder must have a Strength of at least 16. This item appears in Baldur's Gate II: Throne of Bhaal and Baldur's Gate II: Enhanced Edition. It's dropped by Yaga-Shura when he is killed. The weapon can be upgraded by Cespenar, which requires the Rune of Clangeddin and some gold.

In-game description before upgrading
"This darksteel hammer has a rune of power inscribed upon its head, and has many of the powers of a Mace of Disruption."

Upgraded
Runehammer +5 is an enchanted hammer, which inflicts 2d4 +5 points of damage and 4-16 +10 points of damage against undead creatures, plus they must make saving throw vs. with a -4 penalty or be destroyed instantly. The weapon provides the wielder protection from energy from the negative plane, which makes them immune to level drain and immunity to any form of fear. It can also be used once per day to get a strength of 22 for a brief period and to cast Mass Cure.

The hammer gives the wielder a -5 THACo bonus, the weapon itself weighs only 2 lbs and it has a speed factor of 0.

In-game description after upgrading
"The Rune of Clangeddin is now inscribed on the head of this hammer, granting even greater powers to any who wield the weapon."

Legend
! = after upgrade.
 * 1) = before upgrade