Warning: contains spoilers for One-Punch Man Chapter 146
The transformation of One-Punch Man's Garou into a monster has been a long and drawn-out process, and it hasn't been clear just what the end result would be. But in chapter 146, the monsterized Garou has not only had his physical abilities improved but he's also had one of his biggest handicaps stripped away, creating a far deadlier foe than even Garou's former master was expecting.
Following the destruction of the Monster Association's base, Garou was missing in action for quite some time, until he finally arose from the rubble in a sinister-looking new form. No longer able to speak, the monster Garou went wild, first attacking Bang's brother, Bomb, and even attempting to strike out at uninvolved parties like Blizzard, who's been left on healing duty. Bang finally managed to extricate himself from the battle with the other monsters to fight Garou head-on, as he's carried a feeling of responsibility for the young man's rampage.
The fight between Master and student gets off to an impressive start, as the old man proves why he's the third-ranked hero in S-class. Bang notices quickly, however, that there's more than just increased reflexes, speed, and strength on Garou's side: he's still learning, growing, and improving at a shocking pace. In fact, Bang muses that Garou is a far better student now, despite his monstrous form, than he ever was as a human at the dojo.
As Garou's background and history have been unveiled, one thing that's become clear is that Garou's natural talent made him arrogant. It's why he's challenged S-class heroes, even while horribly injured, and it's what led him to leave Bang's dojo before his training was officially complete. The intensely egotistical behavior he's had on display in every fight is the flaw that's always been present in his character, even when he only narrowly survived, like after his match-up with Tanktop Master or when the lower-ranked heroes cornered him outside the kid's clubhouse. Holding such a high opinion of himself and coming out on top, again and again, seems to have almost fueled his monsterization, as he became less and less human after each fight. Intense feelings are known to be part of the cause for transforming into a monster, as seen with Homeless Emperor and Phoenix Man, so Garou's ego may very well have been the catalyst.
The monsterized Garou, however, seems to have lost all sense of self, unable to communicate and showing little in the way of higher brain functions outside of what's needed to fight. While it seems counterintuitive at first, this was really the only way left for Garou to improve: by losing his humanity, he's no longer held back by his pride and his ego, and he instead learns from each attack rather than feeling it beneath him. The human Garou would never have used Bang's own techniques against him in a fight, but this monster version will, and that makes him a far, far greater threat than ever before. Then again, will Garou's victory in One-Punch Man have any meaning if there's no longer enough of him left to enjoy it?