Alongside a variety of new content on the cosmetic front, like Pets and skins, Season 6 of Fortnite: Battle Royale has changed up gameplay in a number of ways. The map has been altered, and Epic has introduced something called Shadow Stones. You can see them in action above.
When consumed, Shadow Stones allow you to go invisible when standing still. On the move, you get other buffs, such as the ability to move more quickly and to phase through certain objects. However, this comes with the downside of being unable to fire your weapon.
A glitch actually allowed you to shoot your gun while invisible, causing Epic to briefly remove Shadow Stones from the game, but they have since returned, and you can dive into Battle Royale for yourself right now to check them out. They aren't in fixed locations, but you'll tend to find them in the new corrupted areas.