The Lightfall campaign does not have a lot of puzzles. You will spend most of your time learning about Stand, wishing you knew what The Veil was, and power leveling. There is a small puzzle, however, that you will need to solve in the Headlong puzzle, near the end of the campaign. This guide will help you learn everything you need to know about solving the Headlong puzzle in Destiny 2: Lightfall.
In the Headlong mission, you will need to enter the Thrilladrome (Lost Sector) in the Liming Harbor. However, after arriving in the area, you will see that the entrance to the building is blocked by a Vex barrier. To remove this barrier, you will need to solve a little puzzle involving some Vex Harpies.
After reaching the barrier, kill the enemies until you see a few Vex Harpies spawn. Instead of killing these Vex Harpies, make a note of the crystals above the barrier. Some of these crystals will be glowing while others will be non-glowing. This is the order you need to kill the Vex Harpies in. Now if you see the Harpies, you will see that some are also glowing while others are non-glowing. For example, if the crystals on the barrier are non-glowing, glowing, non-glowing, you will need to kill a non-glowing Harpy, a glowing Harpy, and a non-glowing Harpy.
It is also recommended to wait a couple of seconds after shooting a Harpy so that it registers properly. After the barrier is removed, progress ahead until you come across another puzzle. Simply repeat what you did before to remove the barrier.
After a while, you will come across a third iteration of the puzzle which is a little complicated. This time you will have normal Harpies, nonglowing Anion Harpies, and glowing Cation Harpies. The only thing you need to remember is that normal Harpies do not have any purpose. For the non-glowing crystals, you will kill Anion Harpies, and for the glowing crystals, you will need to kill Cation Harpies.
Hopefully, this helped you solve the Headlong puzzle in Destiny 2: Lightfall. If you have further questions, be sure to let us know!