Any way to embed a report into another report?

The visual sandbox is the generic host that Power BI uses for executing any custom visual. It is not a specific type of chart in this context and is named sandbox in the DOM, mostly due to fact that it is a sandboxed iframe that prevents code inside it from accessing the main Power BI window and keeps the visual isolated.

Certified Power BI visuals are visuals in AppSource that meet certain specified code requirements that the Microsoft Power BI team has tested and approved. The tests are designed to check that the visual doesn't access external services or resources.

To view the list of certified Power BI visuals, or to submit your own, see Certified Power BI visuals.