Wet Bomb

A liquid bomb throws like an ordinary bomb but leaves the terrain alone. Instead of a crater you get a patch of liquid: the Wet Bomb lays water, the Lava Bomb lays lava, the Honey Bomb lays honey, and the Dry Bomb deletes whatever is already there. They also trigger on contact with any of those three liquids rather than waiting out the fuse, so a bomb tossed into a pool goes off the moment it touches the surface. Shimmer is the exception: they bounce off it and nothing happens.

You cannot buy your first one. It has to be fished out of lava, in an Obsidian Crate or a Hellstone Crate. Once one is sitting in your inventory, the Demolitionist will start stocking Wet Bombs, and buying a supply of those is what unlocks crafting the other three. The same rule applies to each type: hold one and he sells that one. All of which means the single habit that matters here is never using your last bomb of a given type. Spend every one in the world and the only way back is another lava fishing trip.

The obvious jobs are the ones that would otherwise mean hauling buckets: filling a fishing pool, flooding a lava pocket to seal it in Obsidian, draining a room you accidentally flooded, carrying honey up out of the Jungle for a healing pool. Watch what you are standing in, though. If you are fully submerged in the liquid a bomb places, nothing happens at all. If you are submerged in a different one, most of the new liquid instantly turns solid on contact, becoming obsidian, Aetherium Block, Honey Block or Crispy Honey Block depending on the pairing. That is a fast way to manufacture blocks and an equally fast way to entomb yourself.

In Hardmode the Cyborg sells Dry Rockets, which start the same chain again for launcher ammo and give you the effect at range. One niche use worth remembering: in For the Worthy worlds a honey placement will slow Golem to a crawl, which takes a lot of the pressure off that fight.