The rival system is a recurring mechanic in the Mario Kart series where one or more computer-controlled opponents are given a massive advantage to ensure the point standings in the tournament grid are always close. Some implementations of the system may also dictate the rank order of the entire grid and not just the CPU closest to the player. It is usually enforced through rubber band AI, a racing game convention where opponents get a speed boost (often beyond what the ingame statistics for the character would allow) when they fall too far behind the player. Rival characters may be given other advantages such as recovering faster from hits and getting better item probability.
Super Mario Kart
In Super Mario Kart, rivals contain one very fast driver, one fast driver, one medium driver, one slow driver and three very slow drivers. It is notable that when one of the three slowest drivers gets hit, that kart will keep its place, while when one of the faster cars gets shot, it will usually resume its previous place very quickly unless unable to catch up fast enough before the race ends. For this reason, the drivers (except the human racer) will (if unaffected) always finish in the exact same order. Also, if the player tries to hit an opponent, the opponent jumps over the item a majority of the time. Also, the rivals are not determined in pairs, so that even if Donkey Kong Jr. is Mario's rival, Mario will not be Donkey Kong Jr.'s rival, as shown in the table below.
The rivals for each driver are always the same, the list will be in the order the line up for the first race. It is possible to change the order if the rivals can't recover their place at the end (for example, if someone is playing as Luigi and Yoshi finishes last, Yoshi will then become one of the three slower drivers while everybody takes the next position up). It happens mostly on 100cc and 150cc.
The rivals are determined by the current points standing, meaning that if Yoshi was still only second to the player, he will boost back to first position from the start.
Mario Kart 64
Mario Kart 64 and most of the subsequent installments (beside Mario Kart: Super Circuit) until Mario Kart 7 employ a simpler variation where one or two random opponents are selected at the start of a tournament to be of much greater skill than the other racers. Rival racers have strong rubberband AI.
Mario Kart: Super Circuit
Mario Kart: Super Circuit features a preset order of CPU opponents from slowest to fastest exists for each character in Grand Prix mode. In Quick Run mode, the orders are reversed, except in the first track of each cup. When playing Grand Prix in multiplayer, the rival order depends on the first player's character.
Mario Kart 7
Mario Kart 7 returns to a system similar to Super Mario Kart, although more simple as two characters are set instead of single characters followed by another single character, etc..
Each character's rivals will never change; for example, Bowser will always appear in a Grand Prix if the player is playing as Mario. However, if a set character is supposed to be unlockable, the set character is replaced by a default character until the unlockable character can be used. That will make the default character a third rival that occasionally appears in the race. The only exception to this is Wario, who does not have a third rival due to both of his main rivals being starting characters.
Mario Kart 8 / Mario Kart 8 Deluxe
Mario Kart 8 uses a Rival system similar to its predecessor, with several alterations. A set rival system is present only in the Grand Prix mode of the game; all other modes, including single player VS and battle are not affected and have randomized CPU opponents. Furthermore, only the original characters from the E3 build of the game receive a set system of rivals (Mario, Luigi, Peach, Daisy, Yoshi, Wario, Donkey Kong, Bowser, Koopa Troopa, Waluigi, Toad, and Toadette). The rest of the playable characters do not have a rival system of any sort, and all of their opponents in any modes are randomized. If there is more than one player participating in a Grand Prix, the first player's character determines whether there is a rival system or not, and what specific rivals the game gives the character. If other players choose the rival characters, the rivals are replaced by another, random character.
Mario Kart 8 Deluxe uses the same system, although more characters have been given rivals.