Spoiler on locations:
1/ Crom Faeyr Scroll, tells you how to make it, Shadow Dragon in the Temple Ruins as part of the Umar Hills Quest
2/ Hammer of ThunderBolts+3, Illithid Caves in the City Sewers, needs key from Firkrag's Mage at Windspear Hills
3/ Girdle of Frost Giant Strength, Abyssal Knight in the Underdark in Chapter 5
4/ Gauntlets of Ogre Strenth, Halfling Warrior in the Planar Sphere Quest
The idea is that you can only aseemble these in Chapter 6 into the Crom Faeyr Hammer +5. It kills Trolls, and giants on Touch, and delivers the occasional electrical shock. Oh, did I mention it boosts your strenth to 25 permnantly? Well worth it!
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