Two level transition

Hi, I have been looking for a solution for days. I hope to find it here.
In short, I have two level (Level A and Level B), these levels are the 3d scene preview. I streammed both in a single level, now i must show one level and hide the other based on selected scene on menu, I must do it with a nice transition (As an sphere mask), how can I do? Thanks a lot!

You can do some cool stuff with masks or post processing.

But if you have two levels streamed in, the engine just sees everything as one group of actors, so you’ll have to setup some kind of system to differentiate between them.

This is quite a good example:

I haven’t watched the whole thing, I don’t know what his setup is.