Breakable Blocks
Breakable blocks are the soft terrain of the well — destroyed by shooting them or by knocking them from below with your head. Blocks tinged with the secondary colour (red, in the default palette) drop gems when broken.
Their look changes with the area: dirt in the Caverns, boxes in the Catacombs, coral in the Aquifer. Limbo famously has almost no blocks at all, and a narrow column of breakable blocks forms the final barrier before the Boss.
Landing on breakable blocks ends your combo just like solid ground. With the Gunpowder Blocks upgrade, destroyed blocks fire a Machinegun-strength shot upward — chain reactions included.