The Bluebook 20th ed. by Harvard Law School was published in the summer of 2015. While Harvard does not provide an official reference guide / cheat sheet / summary of the Bluebook (unlike the OSCOLA Cheat Sheet), here are our top two unofficial cheat sheets available on the internet:
1. By Penn State Law (The Pennsylvania State University)
2. By STU Writing Centre
In case of any doubt, mooters are advised to refer the original Bluebook 20th ed. for correct referencing.