Super Mario 3D World includes bonus Luigi-themed retro game

The Year of Luigi is coming to an end. But Nintendo has yet one more bonus to celebrate Luigi's leaner, greener brother. The upcoming Super Mario 3D World includes a readily-accessible bonus that pays homage to one of the earliest entries in the franchise.

Spoilers follow.

Discovered by NeoGAF, GameXplain has a video of Luigi Bros. Accessed from the main menu, this is a Luigi-themed adaptation of the original Mario Bros arcade game. But... who would player two be?