Scarab Bomb

Instead of a round crater you get a long narrow corridor punched away from where you were standing. It sticks to whatever it lands on first, so you can place it precisely, and the direction is locked in at the moment you throw rather than updating to wherever you have run off to. Do not treat that as immunity. Stand near the mouth of the tunnel and the explosion will still take a bite out of you.

• Thrown straight down they dig a hellevator far faster than any pickaxe, and a couple of those shafts double as containment lines against hardmode evil spread.
• Any layered farm comes out clean, since the cut is flat. Herb rows and bulb chambers are the obvious cases.
• Underground desert fossil sits in wide flat sheets that peel off one layer per bomb. The extractinator output from those fossils covers the cost of the bombs you spent, so the harvest funds itself.
• In the dungeon they strip out spike-lined pits without damaging the bricks, because the brick ignores explosives entirely.

The blue flame and purple carapace look lifted straight out of Halo, where a Scarab is a very large digging machine. Whether that is deliberate is anyone's guess, but the resemblance is hard to miss.