Space Gun

The Space Gun is magical weapon crafted from the Flintlock Pistol. It has a fast attack speed and costs 9 mana to fire.

It shoots extremely quick lasers instead of ammunition, which do not require the player to lead their targets. The lasers penetrate enemies (max of two as of version 1.0.5), making it good against crowds. As of update 1.0.3, when you have the full Meteor Armor set equipped, mana cost to use this is reduced to 0. 

Note that the Space Gun doesn't count as a firearm in-game, so if your Arms Dealer is killed, and you don't have another firearm, he will not return until you've gotten a replacement.