The Default GDevelop Template(Platformer) has three extensions that don’t appear on my usual screen. They are Enemy, Player, and User Interface.
My guess, based on the icons for them, is that they’re not available in the Extension “store”, but have been specifically made in the project.
So is there a way to add them into my own project?
Edit them, and then export them.
Double click on the extension, and click the icon in the top right of the page (this one 
)
Select export on the page that pops up.
You can then import them into your own project.
Just for clarity, keep in mind that extensions as a concept are project specific bundles of event logic that you make, such as custom behaviors or functions.
Basically, all items on the extension list are extensions that game devs have decided to submit to be listed. Not all extensions are on the extension list.
In the platformer example’s case, they appear to be some base level events that they just put into custom functions/behaviors to clean up the event sheet.
I’m being pedantic, but while extensions in GDevelop can be created at will for any project without being submitted to the extension registry, extensions as a concept are project independent.
Extensions assume a generic empty context, they are not aware of the project or scenes and cannot access your objects etc unless you use parameters to define what it can have access to from the project, in a generic manner that allows it to work interchangeably with practically any project.
1 Like
No pedantry at all, thanks for adding the further clarification.
I was using project specific as in they exist within the project after creation, which definitely can cause confusion with my wording.