Unity: Testing Multiplayer in Multiple Editor Instances

If you work on a multiplayer project, you’ll sooner or later come to the point where you want to play, test and debug your game locally by running multiple instances of it.

UE4 multiplayer options
In Unreal Engine 4 this is simply done by increasing the player counter.

It just so happens to be that Unity currently doesn’t support this feature out-of-the-box. Many critical comments and curses (while people are raising their fists to the sky in anger) I’ve read in forums and on social media about that, but don’t fret: I’ve got you covered.