The Halruaan Force Bomb is a magical item created by the Halruaan people. When it explodes, it does so with the force of 10,000 Magic Missile spells. This is enough to level a city. 
The Wafflecrew found the bomb, a black egg-shaped device with a glass window, in the wreckage of the Star Goddess after their fight with Artus Cimber. The bomb was in a well-made chest protected by a Glyph of Warding, presumably to avoid the bomb being disturbed, or any jostling that might cause it to explode. Diath opened the chest and took the "egg", at the time not knowing what its capabilities were.
Some time later, the group investigated the "egg" further and discovered its true power, much to their chagrin. 
After the nightmarish events of Episode 79, the bomb was triggered and began to count down. After much panicking, Diath managed to stop the countdown by inserting one of his magical keys into the bomb's keyhole. 
The key remained in the bomb until Episode 92. When the Wafflecrew attempted to barter with Aremag in order to leave Chult, things escalated, and Diath eventually removed the key from the bomb and cast it into the dragon's mouth. Aremag submerged himself before the bomb exploded. The shockwave was felt as far as Port Nyanzaru itself, but the boat and the Wafflecrew were relatively unharmed, riding the shockwave out to sea. The bomb itself is presumed destroyed along with Evil Paultin and the Canaith Mandolin.