Are your walls concrete?
Have trouble sticking things to them?
You need to try E-Z UP Clips!!
I wish I was getting paid to promote these but I'm not.
I've been using these for 20 years and I have no complaints. They will keep items up until you take them down!! They are reusable so you only need a few boxes.
If you like the monsters click the pic to order from her TpT store.
You slide the clips on what you want to put up and then push them onto the wall and Wahla!