
Youkai Academy has one in Big Human on Campus. Wynonna Earp: In #3 of the IDW series, Wynonna breaks up a paranormal fight club being run by demon/human hybrids. Such fights can simply be for fun, to blow off steam, or even to resolve disputes. Nubia & the Amazons introduces the Victor's Circle, a secret, quasi-official club that has existed on Themyscira for thousands of years where Amazons, regardless of rank, can meet to have unarmed fights. Obviously, this would put her at even more of a risk. Moon Robinson in Wonder Woman (Rebirth) did this before becoming Mayfly, as a way to not let her hemophilia confine her life. Also, Cy-Kill, who in fine Hasbro tradition was shown getting scrapped by Megatron. Notable contestants (beyond Megatron himself) included Grimlock, Overlord, and Scorponok. The Transformers: Megatron Origins had Megatron establish an underground gladiator arena where lower-class bots could engage in illegal fights prior to the outbreak of the Cybertron Civil War. Thunderbolts had a bizarre period at the end of its original run when it became a book about an underground fight club for supervillains. Robin Series: "The Legless Master" (one of Tim Drake's martial arts instructors) and his brother "The Armless Master" (one of Selina Kyle's martial arts instructors) made a name for themselves in the underground Thai fighting circuit in their youth. Dave Clark, who later become the superhero Midnight, earned a living during the Depression by travelling around the country as a bareknuckle boxer. Batwoman: Kate Kane and Sophie Moore conducted a private one during their last year as West Point cadets, meeting alone and in secret for an illegal bare-knuckle boxing match. The two gangs at the center of 20 Fists seem to exist for no other reason than to get into huge fistfights with each other. BOXEE LIVETV SERIES
X, being a much bigger jerk than his predecessor, is the one who sets these up and even arranged the one seen in the series to have a Killer Robot as the lone Gatekeeper. Provided they survive the battle royal and defeat the Gatekeepers, again with bored rich people betting on the outcome.
Tiger Mask W has Hell in the Hole, an event where the new Tiger's Den disgraced wrestlers are offered a chance to get out of their horrible punishment and back on the ring. X is appalled by them as soon as he sees them and what they're entertaining themselves with while they wait for the fights in Tiger's Cave Paris club. In a variant, it's not the club to get demonized but the patrons, rich and bored people who bet on the fights and on who's going to die. This is Adapted Out of the Lighter and Softer anime, with the fights there recast as normal fights on legal rings. Tiger Mask has a brief period fighting in these after reverting to Tiger's Cave-style assassination moves in the fight with Red Death Mask, as he feels he'd be too dangerous for normal wrestlers if he fought on normal rings before getting himself back under control (in a rather humoristic variant, Tiger Mask goes in Tiger's Cave Paris club knowing they'd shoot him the moment they confirmed his identity, confiding in the situation being so ridiculous they won't even consider him being the real deal until he's already on the ring and their own rules forbid them from unmasking him until he's defeated). Needless to say, the location is never once brought up after its debut episode in favor of showing other trainers with Rockruff's evolutions. That's where dozens of wild Pokémon fight each other-among them, the Rockruff that stayed with Professor Kukui. In the Pokémon Sun and Moon anime, a pair of Lycanroc, a Midday and a Midnight, appear to run a Pokémon Fight Club at a place called Clawmark Hill. The sequence feels a bit absurd because Mike and all the other characters are penguins.
Penguin Memories features a sequence where the main character Mike, suffering from PTSD after dealing with the horrors of The Vietnam War, becomes a drifter who participates in underground fighting rings to get by until he finds a life he wants to lead. Their leader is even named Tyler Nyaaden. Parodied in Kamichu!, in which stray and domesticated cats gather at an abandoned factory to train in martial arts so that they can protect themselves from humans. They use to modify and strengthen their own style of martial arts. It is a place where experts in karate, boxing, wrestling and any other martial arts gather. In Battle Club there is the Nightmare of the Battle NOB in short, a group of fellow highschoolers only interested in strength.