The Terrain Liquification Gun(or TLG) shoots a laser that liquifies the ground where it hits as long as the laser hits the ground. Mobs and Players can fall through the ground while it is in this state. Combat ApplicationsReleasing the laser instantly resolidifies the ground it is liquifying which means any players or mobs that have fallen through will be trapped and suffocate. This application would be particularly useful when fighting a large number of ground mobs at once. The player simply holds down the laser until a sufficient amount of mobs have fallen in and than releases it to suffocate them. Exploration Applications When aimed directly below the player he\she will fall through the ground until the laser is released. This makes it possible to travel straight down very quickly. This means that the player can spend more time mining and exploring and less time looking for caves.
I think there would be some substances that it could not liquify such as wood, ores, and other complex substances
A different version of this gun could get around the liquids problem by just "Phasing out" the object, making it fade and allowing people to pass through it.
And then you could use the liquid stuff as rocket fuel or something of the sort if you tried to liquidize a coal source or something.
I think that you should only be able to phase through simpler materials to make it not the uber-tool. I also think it should be an energy weapon (limited by the player's energy). This would also mean you couldn't go all the way down using this without suffocating (if that's a thing), but you could open up gaps down or to the sides pretty fast underground. Because they're liquid, it's also be pretty easy to shave materials off of the ceiling, because of gravity.
You also have to keep in mind that when the material ceases to be affected by the gun it resolidifies. This keeps the wepon from being an uber tool because you have to be cautious or you will end up trapping yourself in a stone wall. Also...I just realized that this could be used as a greifing tool. There would also have to be an option to limit its use on homeworlds.
I counted this get stuck part for why "limited energy" stops this from being an uber weapon. You'd get stuck when you ran out of energy.