Stalagmight Geode
This snapped-off rock formation has a cache of magical, growing crystals inside it. You gain a +1 bonus to attack and damage rolls made with this magic weapon. When you hit a creature with this weapon and roll the maximum number possible on the weapon's damage die, the crystals rapidly grow and increase the weapon's damage die by one size, up to a d12. For example, when you roll an 8 on the weapon's normal d8 damage die, its damage die magically becomes a d10 after the attack. Immediately after you roll a 12 on a d12 damage die in this way, each creature within 5 feet of the greatclub (other than yourself) must make a DC 15 Dexterity saving throw. A creature takes 1d12 piercing damage on a failed save, or half as much damage on a successful one, as the weapon's crystals explode into shrapnel. Once the crystal explodes, the weapon's damage die becomes a d8 again.
Deep in the Direstone mines, cave trolls linger and carefully collects trinkets from the neighboring dwarven city. Their patience has been rewarded, over time, with a distinguished appreciation for craftsmanship and culture. Despite their grizzled appearance, these trolls have more sense than their average surface brethren, and know that it's often better to barter than to brutalize. At first, at least. Of course, the urge to find and hoard gemstones, much like their adopted dwarven interests would suggest, can easily become overpowering. As a result, some of the most prized possessions among the Direstone trolls are what they would consider "practical gemstones" — ones large enough to smash into an unsuspecting dwarf.