This command block will allow you to call an alien aircraft, which will generate hostile aliens, after killing which you will be able to get a Blaster and create an electric sentry. This will only work on snapshot 16w21b and higher.
How to use Aliens
- Download and install all
- Copy the command text from a file (Ctrl+A -> Ctrl+C)
- Launch the game and get a command block, to do this type in console /give @p command_block
- Put the command block on the ground
- Click on it right click and paste the command in the “Command console” (Ctrl+V)
- Activate the command block using the button or the lever