In his prime, Donnie stood at 5 feet 8 inches and weighed 165 pounds. Donnie Yen is known to be a very well-built and muscular actor. Within the Hong Kong cinematic industry, Yen is renowned for his physical fitness, strength, and speed achieved through his use of a strict and disciplined fitness regimen to build up strength and fitness.  However, despite his muscular build, Yen has gained tremendous attention for his dedication to his roles and for the lengths to which he goes to achieve the physical build and appearance of the characters he plays. In 2007, Yen lost over 30 pounds to reach the weight of 120 pounds to better portray the slender Ip Man and the techniques of wing chun, which focuses on techniques and not strength. He did so through a very strict regimen of limiting himself to one meal per day.  In 2010, still fresh off Ip Man 2, Yen was cast as Chen Zhen in Legend of the Fist: The Return of Chen Zhen, which was originally portrayed by Bruce Lee. He had to regain his muscular physique for the role and took 6 months through a very delicate and dedicated diet routine. Focusing on high-protein drinks and vitamin and mineral supplements, he managed to hit 165 pounds for the role. He maintained this bulk and physique while filming The Lost Bladesman, in which he plays Guan Yu, a Chinese general known for his size and spear-fighting abilities.  In 2015, Yen reduced his muscular physique yet again to reprise the role of Ip Man in Ip Man 3 and for his role as the blind warrior monk Chirrut Imwe in Rogue One: A Star Wars Story. For his role as Xiang in XXX: Return of Xander Cage opposite Vin Diesel, Yen rebuilt his physique.

Answer this question "Which was his most drastic transformation?" by extracting the answer from the text above.
In 2015, Yen reduced his muscular physique yet again to reprise the role of Ip Man in Ip Man 3