Handcar Havoc is a 2-vs-2 player mini-game found in Mario Party and Mario Party 2.
Gameplay
Two teams have to race using handcars. Repeatedly press A to speed up and B to brake. In a curve the handcar has to be leaned to the left or right so it will go without losing speed. Leaning too much will result in the team falling down into the lava (or falling off the cliff, in Mario Party 2). The first team to reach the end wins.