How do you play as luigi in super Mario world 2?

Answer 1

There is no real way but there are mods out there you can get to hack into the game and use a color mod to change Mario's colors to Luigi's.

Answer 2

sometimes at the beginning of levels luigi will be standing there. you talk to him and he sez want to switch bro? and you say yes. but he is not at the beginning of all the levels, only a few