Engine classes are a key gameplay mechanic in the Mario Kart series, similar to difficulty levels in other games. In Grand Prix mode, you must select the engine class you wish to compete in. The higher the engine class, the faster all karts (including players' karts) go, and the more aggressive the AI racers are. There are four engine classes in all: 50cc, 100cc, 150cc, and the unlockable Mirror Mode, which is only available after getting a gold trophy in every 150cc cup. In Super Mario Kart, 150cc is only available after getting a gold trophy in every 100cc cup when Mirror Mode did not exist at that time. In Mario Kart 8, 200cc is introduced as the fifth engine class.
At 50cc, the AI racers do not drift much and rarely (if ever) perform mini-turbos. Most will spin out on the starting line, and they otherwise do not drive or use items efficiently. As the engine class increases, however, the AI will start to become more aggressive, drifting along the inside of turns, holding items behind them to block incoming attacks from other racers, performing Rocket Starts more often, and generally driving better and becoming more difficult to defeat. Quite amusingly, though, drivers in 150cc are more prone to hitting track obstacles, possibly as a way to balance the difficulty.
Mirror Mode appears in all the games, except Super Mario Kart and Mario Kart: Super Circuit. As its name implies, it "mirrors" all the tracks (even retro courses), reversing all the turns. In Mario Kart 64, it was known as "Extra" mode and was played in 100cc. However, in Mario Kart: Double Dash!! and onward, it became known as Mirror Mode and is played in 150cc. Also in Mario Kart: Double Dash!!, there was also supposed to be a Reverse Cup, where the gameplay was very similar to MK64's Extra mode, but was scrapped before the game was released.
- The term cc as used in the names of different engine classes stands for cubic centimeters, and refers to the engine displacement of an internal combustion engine (such as the ones used in go-karts and cars). The larger the engine displacement, the more powerful the engine is. The average modern economy car has an engine displacement of about 1400cc to 1800cc.