Hey, so about a week ago, I posted this idea onto the forums: http://www.scp-wiki.net/forum/t-1777030/scp-idea
I made that post in a rush because it was the last day I could use a computer for a while, so the idea isn't really complete there, but now I am back with a more updated, better idea.
I am going to keep the alternate universe concept because I feel that there a lot of good story potential with it. However in my earlier post I said you get to the alternate universe through a shed; looking back, I don't think that is actually a good way of transportation as it would be hard to explain why the shed has those powers. Instead you will get to the alternate universe through a mysterious hole in the ground located in an area mainly isolated from civilization. Those entering need to do so by flying some mini-plane into the hole. Upon entering you will be in the parallel universe above the clouds in the sky in the same area as where the hole is located, but with no indication of how you got there. To re-enter into our universe you will need to go through the same mysterious hole located in the alternate universe, and you will enter in the same matter as before.
Now time for the three ideas, which are three ways in how this alternate universe is different to our universe.
Idea 1: Same change I said in my original post, where all forms of life are replaced by forms of life seen in X cartoon series (I will decide which cartoon is best to use if this idea is chosen). Most people (Everyday people and celebrities) are replaced by the good guys from the cartoon series and will treat visitors from our universe with curiousity and respect and will not be hostile unless provoked first. However some people (Those who partake crime and terroristic actions) will be replaced by the bad guys and will go after visitors from our universe for experiments and other bad stuff.
Idea 2: In this parallel universe, all relationships are reversed, and personalities are also changed accordingly. For example, your best friend and lover will be out to kill you, and your most hated person (Your childhood bully, your ex) is now your best friend or lover. In a celebrity view, infamous criminals are now respectful celebrities, and well-liked celebrities are now hated criminals. In an SCP view, SCP-682 is now a well-loved creature that provides a positive impact in its interactions with others, and SCP-999 is now an evil, hated entity that wants to destory all of humanity.
Idea 3: This parallel universe is kind of… darker in a way. An explosion-filled disaster occurred about 20 years ago, sending everyone into hard times. With this, everyone's personalities are darker and to the very extreme. For example, someone who is shy is now so depressed from isolation that they are… snapped. They believe they are not worth being treat nicely to, and will even respond with violence if one were to try to be nice. Someone who is nice and caring is now so worried for the safety of others that they will go to extreme lengths for protection of them. Yes, this includes even violence to force others into submission of their safety. Other examples include someone who is smart becoming a rude smart aleck. Someone who is comedic now uses dangerous pranks that often hurt and sometimes even kill those who are pranked. And someone who already isn't so nice is now even darker, with any signs of goodness inside being harder to spot and exploit for someone who is trying to be friendly with everyone. In addition everyone is generally stronger and the landscape overall is more depressing-looking and dangerous to traverse, to further illustrate the dark theme of the world.
And those are my 3 ideas. If you were to ask me, I would say idea 3 is my personal favorite, but my perspective on the ideas will most definitely be different from others, so be sure to give me feedback. Thank you!