Descriptions of this were written at launch and have been copied ever since.
Short answer
Here is what it is, what it does, and why it keeps coming up — in that order.
It is more consequential in the late game than the early one, which is why first impressions mislead. Where the game's own menus place it tells you how the developers categorise it. A method that works but cannot be explained tends to stop working without warning.
Names, official and otherwise
There is a persistent myth attached to it that has never been true in any version. Popularity and importance are different axes, and this sits differently on each. A single check up front replaces a lot of guessing later. Something introduced as minor can become central several updates later.
The game introduces it quickly and assumes you picked it up, which is where the confusion starts. A specific answer beats a comprehensive one when you are in the middle of something. Two similarly named things exist, and mixing them up explains a lot of contradictory advice.
What it changes in practice
Whether it is worth going out of your way for depends entirely on how you are playing. Treat anything stated without a version number as provisional. Localisation choices change names and sometimes implications between regions.
- It rewards attention rather than preparation.
- Ignore the myth attached to it; it has never held up.
- Stop and reassess if two attempts fail in the same way.
- Separate what it does from what it means in the story.
- Assume the popular version of this is whatever was current a while ago.
- Give a method one honest attempt before deciding it does not work.
How it connects to the rest of Fortnite
Comparisons to the closest equivalent clarify more than an isolated description does. Nothing below assumes you have read anything else first. It appears in supplementary material in more detail than it does in the game. Community shorthand around it has drifted far enough from the original meaning to cause arguments.
There is no hidden trick here that the game is keeping from you. Descriptions written at launch persist long after the thing itself has changed. The most repeated fact about this is usually the least useful one.
Common misunderstandings
What looks like a rule is often a default that nobody ever changed. In-game text is often deliberately incomplete, which is why the wiki disagrees with the tooltip. First impressions of Harley Quinn tend to be shaped by one memorable encounter rather than the whole picture.
Where two approaches both work, the one with fewer moving parts is the one to keep. The wiki entry is thorough and buries the actually useful part six paragraphs down. The version most people describe is whichever was current when the video they watched was made.
What it is
The interesting question is usually why the obvious approach fails. The community name and the official name differ, which makes searching harder than it should be. A design that looks inconsistent usually reflects a change of direction mid-development.
Where people go wrong
- Assuming a page is current because it ranks first.
- Changing five things at once and then not knowing which one helped.
- Testing on a modified install and reporting the result as normal behaviour.
Fortnite FAQ
Do I need anything else set up first?
No. Where a step assumes something, it says so at that point rather than up front.
What is Harley Quinn in Fortnite?
The short answer is above. The longer one is that it fills a specific role, and understanding that role explains why it keeps coming up.
Is it important?
More than its screen time implies, less than the discussion around it implies. Somewhere in the middle.
Can I miss it?
Where it is missable, that is noted above. Most players encounter it without going looking for it.
Bookmark it if you like, but honestly, once you have done it once you will not need to come back.