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Intransigent Warhammer
Intransigent Warhammer
Uncommon
1d8 Bludgeoning
Impulse Blast: You knock nearby foes Prone after killing a hostile target or landing a Critical Hit.
Proficiency with this weapon type unlocks:
The elegant design of this hammer belies its brutal, crushing power. This weapon does not give ground.Warhammers Versatile
Location - Intransigent Warhammer
Located while sailing to 
Grymforge. Will be located on the Duegar skiff inside a chest.
Discussion
You have to fight and kill the dwarfs on the Ship in the Underdark and loot this. So, the dwarf shouldn't leave the ship, if you know what I mean.
Gale can absorb the Magic from this Item. If Gale consumes it, it vanishes forever. That is irreversible and unavoidable.
(There is better food for Gale: Ring of Color Spray, Frayed Drow Hood, Sunwalkers Gift, Everseeing Eye Necklace, Exterminators Axe; Hunting Shortbow, Kormira's Locket, Spiderstep Boots.)