Combine cake mix, orange fanta and egg white. Mix on medium until no longer lumpy.
Add to greased baking pan, top with crushed OREOs, then bake according to cake mix instructions, then let cool.
For the Orange slime, pour Orange Fanta into a small bowl, then whisk in corn starch.
Heat a pan to medium heat, then add Fanta mixture.
Turn up heat and bring to a boil, then turn heat down to low. Let it cook for about 1-2 minutes, stirring often until it thickens. Remove from heat and refrigerate.
While cake and slime is cooling, whip whipping cream in a mixer until it starts forming peaks, for about 2-3 minutes. It needs to be stiff, but don't wait too long or it will turn to butter.
Once it's thickened, add sugar and marshmallow cream and whip until combined.
Pipe or spread whipped topping over cake, top with slime and more crushed OREOs and serve!