Rival Turf has Player 1 in red and Player 2 in blue, allowing both players to use the same character if they wanted to (officially, both Norton/Flak and Bild/Nelson wear red).
Brawl Brothers will allow both players to choose the same character, but only in versus mode. The five main characters each have his/her third color palette for his/her AI-controlled variant.
The Peace Keepers does the same with Brawl Brothers, except up to four players, still only in versus mode. Also, using the shoulder buttons at the versus mode character select screen will change the color palette of which character you're deciding on.
Difficulty By Region: The Japanese versions of the games are easier than the American ones. Here's proof:
Rival Turf had no difficulty settings unlike the Japanese version, and you could adjust the number of lives and difficulty, too.
Brawl Brothers had the sewer become a maze you had to navigate, whereas in the Japanese version you just fought straight through to the boss. Also, in Stage 3, when you board an elevator, you had to choose a certain floor to continue on in the overseas version, while the Japanese version just took you to the next floor.
The Peace Keepers had 12 continues as opposed to the Japanese version's 30.
Distressed Damsel: Rick Norton's sister, Maria, who's kidnapped in the first game. If Wendy wasn't one of the characters you picked in Rushing Beat Ran, you'll need to rescue her in one of the levels. Maria's also kidnapped in Rushing Beat Syura, and Rick can be found on one of the routes.
Dub Name Change: The two main heroes of the franchise; they changed for the first game, changed again for Brawl Brothers, and then got their original names back in Peace Keepers. On that note, Peace Keepers changed all the characters' names abroad (Dick to Flynn, Elfin to Echo, Kythring to Al, Jimmy to Prokop, and Metal Frame to Orbot).
Expy: Rick Norton is Cody, Douglas Bild is Haggar, the enemy types correspond to those from Final Fight, one enemy does the Hurricane Kick, one of the bosses is Vega, the final boss shoots out Hadoukens from his mouth, one of the characters from the later games fights like Guy, and on and on.
Rival Turf averted this so executing desperation attacks requires 5 points from your body count, which is located above your life meter and increases by one for every enemy defeated.
The desperation attacks in Brawl Brothers all pose as "offensive special" ones from the Streets of Rage series, meaning that they will drain a small amount of your health when performed, whether it hits or misses. However, wait long enough without being hit or reusing the special attack, and that health may recharge.
The Peace Keepers utilize the traditional "defensive special" moves, so whenever these hit an enemy, a small portion of life will be sacrificed.
Limit Break: Angry Mode, which makes you invincible and more powerful after you take enough damage from enemies. The other Limit Break appears to be the character-specific "Termination Skill" in The Peace Keepers, which destroys all on-screen enemies. However, Norton's Termination Skill gives him an instant Angry Mode while Orbot doesn't have a Termination Skill at all.
Turns Red: The final boss in Rushing Beat/Rival Turf turns red a few times throughout the battle if you damaged him enough. He becomes more powerful and invincible too, so it's his version of angry mode.
Unfortunate Names: Rick Norton and Douglas Bild were renamed Jack Flak and Oozie Nelson in Rival Turf.
Not that their overseas names in Brawl Brothers were an improvement — Hack and Slash.
Wrestler in All of Us: Especially when in angry mode, where throws are more over the top and more powerful than ever.