Warning: contains spoilers for the latest chapter of One-Punch Man
The monsters of One-Punch Man had surprised many by setting aside their differences and egos to form the Monster Association, but without the strong leadership provided by Psychos and Orochi, their days of organized evil are seemingly numbered. Even with the common enemies of the S-class heroes and their allies, the biggest monsters in the Monster Association are finding themselves at each other's necks, and it's only looking worse in chapter 146.
The cooperation between the Monster Association's executive members had already been tenuous, as many of them had conflicting ambitions and were merely biding their time until the heroes were taken care of. Some were no smarter than animals, like the gluttonous Gums, who first came into conflict with Fuhrer Ugly after being struck by a redirected attack. Fuhrer Ugly eventually killed Gums, but not before he was partially digested by the monster's stomach acid. While this resulted in some unexpected power-ups for Fuhrer Ugly, it's also left him melting and falling apart, ready to eat anything and everything he comes across to avoid losing too much mass.
Of course, the most convenient source of food around happened to be his fellow monster, the massively replicating (and exceedingly disgusting) Black Sperm. Fuhrer Ugly's threats only increased as he made an offhand comment about farming Black Sperm as "an infinite source of protein," and the two deadly monsters were soon at each other's throats. The countless Black Sperm even combined to create one giant super form, which dubbed itself "Golden Sperm" and became impervious to acid.
The escalating infighting between the remnants of the Monster Association is offering the heroes a much-needed break, especially after the horrifying deaths faced by most of their allies. Heroes like Tornado are extremely worn out, while Atomic Samurai had been left without a weapon, and others like Blackluster and Tank Top Master are injured beyond the ability to fight. Even if Golden Sperm and Fuhrer Ugly destroy each other, things won't quite be over, as Homeless Emperor has yet to even demonstrate his true power and Evil Natural Water is still slowly lurching towards the ocean--something that could provide it a potentially apocalyptic increase in power. There's also the freshly monsterized Garou to worry about, someone who's already proven to be a chaotic element aligned with no one.
It's hard to assess where the battle stands at present; while far more heroes have died or been defeated than top-level monsters, there are fewer monsters than heroes. On the other hand, many of the remaining monsters have yet to demonstrate the full extent of their powers, and it's been hinted that these are perhaps the most dangerous of all. There's also the mystery of some of One-Punch Man's most powerful heroes: the top-ranked Blast, Saitama himself, and Flashy Flash, who teleported away and haven't been seen in quite some time. With these powerhouses able to potentially appear and join the battle at any time, the balance of power in this fight is far from settled.