Injustice 2
75 Achievements
153-209h
Only A Real Master
Beat an opponent online while they still have 90% health and you have 10% or less health remaining
0.6%
How to unlock the Only A Real Master achievement in Injustice 2 - Definitive Guide
I can confirm that you can do this in an Online->Private Match. Your friend should wear you down to near death. When you start getting close, it's best he use basic jabs by pressing the square button without directions. Once you're nearly dead, he should stop fighting and then you win the match by any means.
(Online)
Easily boostable with a partner in a Private match, KOTH or versus work for this trophy, once you have your partner and after selecting the fighters your rival need to leave your health with a very short bar left, having your opponent with full health. Simply make your way to comeback and win the fight, the trophy will pop right away. Just make sure you do this in the second round of the match because trying in the first one doesn’t work. If you need a partner you can ask for help in the Boosting Thread.
A struggle to get legit. Best to find a boosting partner and invite them/meet them in a room. Then have them beat the heck out of you until you are low/critical and then start the comeback win.