Heroes vs. Monster Association Executives

From here on out it's a free-for-all. Most amount of S-Class kills gets to lead, how 'bout that?

Heroes vs. Monster Association Executives is the battle between the heroes Zombieman, Sweet Mask, Child Emperor, Atomic Samurai, Iaian, Pig God, Tanktop Master, Tatsumaki, Bang, Genos, and Superalloy Darkshine against the Monster Association Executives, Homeless Emperor, Black Sperm, Fuhrer Ugly, Evil Natural Water, and Gums.

Prelude
While Tatsumaki confronts Psykos and Orochi, the other Monster Association executives are locked in their one-sided battles with the heroes. Tatsumaki interrupts each encounter by shielding the heroes with energy barriers and bringing them to the surface, leaving the executives behind. The heroes help Tatsumaki defeat Psykos and Orochi, with the Monster Association base being destroyed in the process.

Presuming their foes all destroyed, the heroes anticipate victory. However, all of the executives are revealed to have survived, and reach the surface immediately after the last battle concludes, taking the heroes by surprise.

Battle
Homeless Emperor arrives on the surface and immediately unleashes a barrage of orbs against Zombieman, taunting the hero's claims about humanity. He derides Orochi and Gyoro Gyoro for their defeat, giving Sweet Mask an opportunity to attack, only for Black Sperm to burst out of the ground and grab the hero mid-air. Fuhrer Ugly arrives immediately afterward and unleashes a Face Crushing Punch on Sweet Mask, before splitting him in two and tossing him away. The three executives agree to compete with each other for the title of Monster King, with the goal being the most S-Class kills. Child Emperor tries to drag Zombieman to safety and alert the other heroes, but is spotted by the monsters.

Fuhrer Ugly steps on Zombieman's regenerating body and taunts Child Emperor while readying a punch, but is interrupted by a massive orb launched by Homeless Emperor. The orb impacts the ground in a massive explosion, with Atomic Samurai, Iaian, Pig God, and Tanktop Master, as well as Fuhrer Ugly, only nearly avoiding it. Atomic Samurai tries to contact Child Emperor, who seemed to have been caught in midst of the explosion, but gets no response, just as Evil Natural Water emerges from the ground. Iaian immediately recognizes the threat and readies his sword in fear. Pig God and Tanktop Master are similarly barely able to avoid being eaten by Gums, who bursts forth from the rubble.

Homeless Emperor, Fuhrer Ugly, and Black Sperm quarrel with one another, but agree to temporarily work together as they head out to confront the rest of the now disoriented and split up heroes. Elsewhere, Genos arrives back on the surface (having been abandoned by Drive Knight) in danger of exploding, but is rescued by Fubuki, who manages to cool his overheating core. Puri-Puri Prisoner sets off to find Child Emperor beneath the rubble, while the rest of the heroes bear witness to the carnage. Homeless Emperor targets the weakened Tatsumaki with a massive barrage of orbs, but is disappointed to learn that his target was yet another of the esper's rock decoys. The real Tatsumaki, waning from her injuries, arrives and insists that others leave the battlefield, ignoring her sister's concerns over her injuries and pleas to help out. Tatsumaki departs alone, but the unswayed Genos and Bang follow after her in support, leaving Bomb behind to watch after Fubuki, and keep an eye out for the still-at-large hero hunter. Tanktop Master and Pig God struggle against Gums even working as a pair, and are caught off guard when Fuhrer Ugly discovers the unconscious members of Narinki's Private Squad, Bushidrill, and Okamaitachi. Taunting the two heroes, Fuhrer Ugly lifts the barely conscious Sosshi into the air before tearing off his arm. Gums takes advantage of the shock to bite down on Tanktop Master, while Fuhrer Ugly throws a punch to finish off Sosshi. However, his arm freezes before it can crush the mercenary, having been stopped by Tatsumaki. Pig God leaps into Gums, freeing Tanktop Master, and the tank-topped hero helps Pig God collect the unconscious mercenaries and heroes before throwing them to safety. Fuhrer Ugly frees himself from Tatsumaki's psychokinesis and punches the heroine into a rock, while Tanktop Master leaps into the ugmon monster with his Tank Top Tackle. Fuhrer Ugly counters with a Forearm Caving Punch and Tanktop Master is instantly overpowered with the follow up Full Body Caving Punches beating the hero to near death. Gums eats the helpless S-Class hero as Fuhrer Ugly turns his attention to the seemingly lifeless Tatsumaki. Before Fuhrer Ugly can get his hands on Tatsumaki, Bang and Genos interrupts the fight as Bang kicks through the jaws of Gums and rescues Tanktop Master while Genos incinerates Gums' insides. Fuhrer Ugly quickly jumps in front of Bang and launches Face Caving Punch, however Bang is able to counter the punch easily and sends it back at Fuhrer Ugly's face. While the two heroes are checking on Tanktop Master's condition, Gums launches a surprise attack at Genos and entraps him within his jaws. Fuhrer Ugly once again challenges Bang with his brute force, launching Dignity Caving Punch, but once again, the punch was easily countered and sent right into Gums while Bang launches a flurry of attacks at the helpless monster. Genos and Bang finally escapes with Tatsumaki and Tanktop Master, both of whom are heavily injured. Gums becomes enraged by Fuhrer Ugly's misaimed attack and proceeds to swallow him. The two monsters engage in a brief scuffle before Fuhrer Ugly tears Gums in two from the inside out. Covered in Gums' digestive juices, Fuhrer Ugly becomes Vomited Fuhrer Ugly. Appalled by his increased ugliness, the dismayed monster swears revenge on Bang. Meanwhile, Atomic Samurai and Iaian fight to repel Evil Natural Water's jets. Finding regular sword techniques to be useless, Atomic Samurai struggles to think of a method to defeat the mysterious being, while Iaian worries what would happen if the monster reached the ocean. Just then, Iaian's sword is finally destroyed by the jets of water leaving him defenseless, but as another barrage is about to hit the hero, Superalloy Darkshine interposes himself between Iaian and the attack. Darkshine is completely unharmed, and takes on more of Evil Natural Water's attacks, comparing them to a pleasant shower after exercising, before blowing the mysterious being apart with a single punch. While Bang and Genos continue their retreat, Black Sperm catches on and throws several attacks in a wall formation, intent on stopping them. Bang is able to deflect the punches, but Genos takes the brunt of the attack and is nearly sent into a chunk of debris, though he lands safely as a timely Atomic Slash turns the debris to dust. With Evil Natural Water dealt with, Atomic Samurai catches the attention of his "special blade testing monster," who in turn taunts the hero for trying to fight him a second time. This time, however, Atomic Samurai uses the blunted edge of his sword to make incomplete wounds on Black Sperm's body, dealing damage while preventing him from multiplying. More of Black Sperm's clones chase after Bang and Genos, but Tatsumaki promptly regains consciousness and freezes the monster's bodies mid air, giving Darkshine an opportunity to obliterate them. Bang, Tatsumaki, and Darkshine join Atomic Samurai in staying behind to fight Black Sperm, while Genos rushes Tanktop Master to Fubuki. Darkshine taunts Black Sperm for his lack of "shine," but the monster is only annoyed - even while facing four of the top S-Class heroes at once, Black Sperm's only concern is that they're looking down on him.

Trivia

 * With a total of 16 combatants, this fight is tied with Heroes vs. Nyan for the most named characters involved in a battle in the manga.