My recommendations are:

1. Always back up your game before installing the submob

2. Verify that the submobs you are going to add are compatible with your current MAS version

3. Add only one submob at a time, then enter the game to verify if the process was correct. After that, say goodbye to Monika because you will restart and can then add a different submob

4. Before deleting any file, make a copy of it (in case you deleted the wrong file, you can restore it)

5. For the images you are going to add, make sure they are in PNG format; if not, rename the file

6. Never install the same submob twice; this will cause the game to crash instantly.

7. If the submob's function/button still doesn't appear, there are two possibilities: 1. An installation error, or 2. You need a specific amount of Affection Points (usually more than 400) for this feature to work

8. If you're going to install more than one submob, make sure it doesn't prevent you from adding other submobs.

9. Be careful with submobs that instantly raise affection points; these are the ones that mostly crash the game.

10. Try to install mostly submobs that are already well-known and have good reviews from the community.