Gunslinger is a custom Fighter class archetype developed by Matthew Mercer for Dungeons and Dragons 5th Edition when the group converted from Pathfinder. There are two versions of the archetype: a professional version is available for purchase from the Dungeon Masters Guild and a free version is available from D&D Beyond.
Most warriors and combat specialists spend their years perfecting the classical arts of fencing, archery, or polearm tactics. Whether they're duelists or infantry, martial weapons were seemingly perfected a long time ago, and the real challenge is mastering them.
However, some minds could not stop with the innovation of the crossbow. Experimentation with alchemical components and rare metals has uncovered the secrets of controlled explosive force. The few who survive these tests of ingenuity can become the first to create and skillfully handle the first firearms.
This archetype focuses on the ability to design, craft, and use powerful but dangerous ranged weapons. Through creative innovation and immaculate marksmanship, you become a distant force of death on the battlefield. However, not being a perfect science, firearms carry an inherent instability that can occasionally leave you without a functional means of attack. This is the danger of new and untested technologies in a world where the arcane energies that govern the elements are always present.