I am posting this here because I have found very little information about this subject.
Hopefully you will never have to do this, but if you have a Mac in any of the following situations below you may need this information.
Boots to Black Screen after -
1. Failed macOS Upgrade
2. Failed macOS Combo or Delta Update
3. Failed macOS Security Update
4. Failed macOS Reinstall
5. Command Option R fails to boot your T2 Mac to the current version of macOS Recovery. (10.14 is out but the Mac boots to 10.13)
One of the hardest things to do is actually get your Mac to boot into DFU mode with a crazy 4 key startup sequence! You could almost make a bar bet out of it!
EDIT: WARNING! Do not attempt a BridgeOS restore on a macOS Catalina 10.15 Beta system! You WILL brick your Mac. I have edited the article to reflect this. I will test again once 10.15 goes live to see if the 10.15 version of BridgeOS can fix the bricked Mac.