Mechamorphosis represented a form of cybernetic enhancement that the Guavian Death Gang's members were subjected to. Bala-Tik was beginning this procedure sometime following Supreme Leader Snoke's rise to power within the First Order, and he already had a cybernetic left leg.
The first mention of Mechamorphosis occurred in Star Wars: Smuggler's Guide, a book created by Daniel Wallace that was published in 2018.