Getting Started Edit
Go to the "2 players" section of the Options screen to decide whether both players will use the same controller or a separate one. The default option is one controller.
Before starting, both players should also discuss the rules on using controversial warps or exploits within the game (i.e. Bridges, 100K Trip, Plethora Cheat, Infinite Lives Glitch), so an argument doesn't happen later.
If the goal is to see who can beat the game first, the above information comes in real handy. Advancing levels via telepad whenever possible, and restarting rounds to avoid certain death can lend huge advantages in this respect. Be careful, though, as hitting "Give Up" does count as a death, and will cause a turn switch.
Both players' games are completely independent of each other, meaning there is nothing one player can do to affect the other player's game. For instance, if player 1 collects a life from a certain prize block, there will still be a life there for when player 2 gets to that same block.
Game Over/Beating the Game Edit
A player is also allowed to continue even after the other player has beat the game. The credits are identical to the ones featured in the single player mode, with no extra text or screens. Note that the entire credits must play out before the other player may continue.
Exclusive Glitch Edit
There is also a very complicated wrong warp glitch which can only be performed in 2-player mode. It can be used to get record times in individual levels and higher scores. Video one shows the basic process and explanation, while video two elaborates on highscoring potential.