Scenario Characters

With a Scenario block, you can only insert cut-out characters from Articulate's Media Library. It is possible to find the image files of Articulate characters in the published course, and replace them with custom images that use the exact same name. Obviously, though, that doesn't allow for seeing the custom characters while previewing nor in Review 360. 

The sample image you posted isn't a cut-out character (that is, it doesn't have a transparent background). You could certainly use various image blocks with that character. See the "A Simple Alternative" lesson in this Rise course.

Another alternative to using Scenario blocks is to branch the Rise course. This project demonstrates and explains how to do that. 

Also consider using the new Custom and Code blocks to get what you want.