Streets of Rage 2 for the Game Gear is a port of Segas legendary Genesis brawler. Although it removes Max and removes some stages, it adds some new levels and each character has a nearly complete moveset despite the lack of buttons. Like every other Streets game, it also features 2-player simultaneous co-op gameplay.
Super Chinese Land 3 is the last game in Culture Brains RPG/brawler trilogy on the Game Boy. Its basically a re-worked, single-player version of Super Chinese 3 on the Famicom. You travel the world in an RPG style, going from town to town to buy items and talk to townsfolk to take on quests. Then, when you engage the enemy, the gameplay switches to traditional beat em up combat. You also gain experience and level up.
Super Duper Sumos is a GBA-exclusive brawler based on the kids cartoon show of the same name. It features three playable characters and new attacks that are unlocked at certain parts of the story. It also has energy-based special attacks.
Teenage Mutant Ninja Turtles II: Back From the Sewers is a licensed brawler/action platformer hybrid from Konami made exclusively for the Game Boy. Although the majority of the game is an action platformer, there are several brawler segments. Its combat is straightforward yet requires precise timing, and you can play as all four turtles (each of which counts as a life.) If you lose a turtle, you have the chance to fight a guard to free them so you can play as them again.
TMNT on the GBA is based off the CGI film of the same name featuring the Heroes in a Half-shell. Its simple combat is surprisingly challenging and is supported by light RPG and exploration elements. You can play as all four turtles and switch off between stages. There are also a handful of side activities in the form of minigames and shopping.
X-Men: Reign of Apocalypse is a single-player GBA-exclusive brawler based off the Marvel Comics franchise. You can play as Wolverine, Rogue, Storm, or Cyclops. Its combat features an energy-based ultimate attack as well as special techniques with Street Fighter-style inputs. It also has light RPG elements in the form of stat upgrades between stages. Its graphics are smoothly animated and vibrant while its soundtrack is a mixture of rock and techno.