Crinkled Screen

 This is my first post, fyi. I have a Tamagotchi 30th Anniversary and it has a crinkled screen sometimes. It fixes itself, but i’m wondering what it is and what causes it.

I think you mean 20th anniversary... lol. "20th anniversary" can mean either the 20th anniversary mini or the 20th anniversary P1/P2/Originals, although I suppose either way it doesn't matter for your problem. I'm not quite sure what you mean by "crinkled screen". Do you mean the sprites or the paper background in the device? It would help if you could post a picture.

The paper background.

There are a couple of things it could be. It could be the background was accidentally bent when it got put in and thus it is pushing up. Or, perhaps the device was not screwed together tightly enough and the background has some wiggle room. If water or some kind of moisture got into your Tamagotchi - by the factory or some other process - that would also cause the background to get wrinkled. In any event, warped backgrounds are very uncommon but it's nothing too worrying - unless its from moisture - as  all virtual pets can work without a background. Some people even open up their virtual pets and swap backgrounds, which can look pretty interesting.