The Sword Lunge Flying Glitch used to allow the player to be able to suddenly start floating up into the air. If they wanted to float back down, they needed to hold out the tool. This glitch was used in 2008 through mid 2013, when it was finally patched. Oddly, it still sometimes can be performed on games such as Bridge Sword Fight and Auto Duels.
To perform this glitch, a player must needed a sword/tool of some sort that could've lunged when you double clicked. When you double clicked, you would've lunged forward and up a little. But if you double clicked and immediately put the tool you had in your inventory, you would've started to float up without stopping unless you were under a brick. But that's not just all, if you equipped the tool again, you would float down instead of up. Making you able to fly like the Red Balloon or Green Balloon gear. You could've also done this if you pressed Backspace after you double clicked if you were able to drop the tool.
A lot of people didn't really know how to perform this glitch until more and more people started to abuse it on sword fighting games with tools that could lunge or any type of game with a lunging tool.