use your mouse to make platforms for luigi to move on so he can get the star! use a and d keys keys to move, down arrow to make luigi small. w key to jump. r to make luigi turn to his normal size (use if you dont want to be small anymore). space to clear all drawn platforms.
oh and thanks to @babymarioop for original thing and to me for the luigi and mushroom that i reskinned to be a 1up and make your self small and jump and while in air make yourself big at the start of a level to move right well that's what i have to do
