Clentaminator

The Clentaminator can be bought from the Steampunker. It is used to create/destroy biomes and it uses Solution as ammo. It has the same firing pattern as the Flamethrower, and is not stopped by any block. Green, Red, and Purple Solution can be bought from the Steampunker, while the Dark Blue Solution can be bought from the Truffle. The only time you can buy Purple Solution and Red Solution is during a Blood Moon, which spreads Corruption and Crimson. It's the fastest way of spreading the Hallow, Corruption, Crimson, Purity, and Mushrooms.

Tips

 * Do not move your cursor too quickly while using the Clentaminator. Doing so will not get everywhere you are trying to convert most of the time. Move it slowly across the screen.
 * Make a circle with your mouse slowly and stop when you reach back to where you started. You can go a little bit beyond the starting point to make sure you got everywhere. This should convert all blocks visible on your screen. It is very useful for fighting The Corruption and Crimson.
 * If you have an Ice Rod or any other item that emits light that can pass through blocks, it should help you find areas to convert.