How can we combine two Unity projects?

Make a package of Project 2 Scene and in Project 1 import it as a Custom Package.

[work in progress]

Package is an edit time feature that lets you export and import collections of source code and project. Can help you merging two projects and similar questions.

I try in this 2 ways. Making a package of the scene or the entire assets

EXPORTING THE SCENE

1. Close Unity. Make a copy of the main folder "myGame" or "myMenu project1" of the Project where you what your final union merge. In this case make a copy of Project 1 where is the scene "Game Menu"(p.1) and the projects settings are set up. Example: If tree folder is C:/UNITY/MyUnitys/MyGame/Assets/Scene then copy "MyGame" folder. [ MyGame - copy ] So if there is any problem you have a backup.

2. Open Unity, Open Project 2. Then Select the scene "Game Name"(p.2) you want to export, then right click and select dependency in the drop down menu; then in the blue selection right click and in the drop down selection, click in Export package. In version 4.3 ( I think there is a bug ) works better if in exporting package windows you select "none and the you click two times the check box "include dependency". with the check box selected, press "export". It will take time to compress. If it do not work (it gives you errors to import) try next time to click only one time include dependency so the check box is not selected as bool.

3. Just take a look to the manes of all the assets you install from asset store to help in your project (just remember the names of the folder). Here is a problem if there are a lot. In my Version number i pick notes of all assets i install from the assets store into my project.

4. Open Project 1. Import the the asset into Project 1 (from: Assets ->Import Package -> Custom Package).

5. If there is no "Game Name"(p.2) scene file (I think there is a bug in Unity). Return to Project 2 and try one more time. Select "Game Name"(p.2) in your scene folder, then right click and export package and directly "export" button (the check box is selected by default) as a new name. Go to Project 1 and install the new custom package. If the "Game Name"(p.2) is not included but all the files yes, then just make a specific package including only the file scene"Game Name"(p.2).

6. Install in project 1 all the assets necessary from the asset store window that was included in project 2. In my case was necessary to install : Projection Correction.

7. Open scene "Game Name"(p.2) in Project 1 and Play. Look in console for errors. Probably you will need to drag and drop array content to the script and other links messing. Turn off Anti aliasing if you are using HDR on in MainCamera And to set up Input Buttons in Edit -> Project Settings -> Input

EXPORTING THE ASSETS

Is similar to the first way but select the "asset" folder instead of the scene file.

At point 2) select the Asset folder right click and in the drop menu select "export Package..."