Here some Free Printable Invitations for your Monster University . You can use them as well for making cards, photo frames, signs, backgrounds and whatever you want.
If you will use them as labels attached to objects, better if you print them on labels self adhesive paper.
If you want to print them in a poster size, you can use "posteriza" (free download).
Remember to do a right click before saving, for having the image in its best quality.