These are machines which make working in your garden easier. You can get them by clicking on an empty lot outside of your garden. Then a pop-up will appear where you can select the Monsterious Machine of your choice. Then, you will have to finish the construction with materials. You can find materials for building whilst harvesting or by asking your friends to send you some.
When you do not have an empty lot, then please go to the expand menu and click on the empty lots tab to buy another lot.
If your Monsterious Machine doesn’t work; it could be because of a large decoration.
You just need to remove some of the large decorations you have in front of your Monsterious Machines - you will then be able to click on them again.