Bomb Blocks are a common obstacle found in Treasure Trove and Shovel Knight Pocket Dungeon that the protagonist must clear to progress.
In Treasure Trove, they appear exclusively during Plague Knight's boss fights and during Plague of Shadows boss fight. They are black 1x1 blocks that can be destroyed only by Plague Knight's/Plague of Shadows' bomb attacks.
In Pocket Dungeon, it's a stone block with image of a bomb on it. It only has 2 HP but it cannot be destroyed by any normal attacks, only by some sort of explosions, such as Bombs or blasts from Ratsploders, unless one is equipped with the Obsidian Drill Relic, which make it possible to damage the blocks.