It may seem like an easy glitch to master, but you’ll need to complete the game first before latching onto those 1-Up mushrooms in two-player mode, plus you’ll need to follow the instructions Retro Collect have summarised from the above video:
First, you must first take player one’s Mario to the second level of the game and throw away your first life. With Luigi taking over, player two must traverse all the way to World 5-2 and find the hidden beanstalk block halfway through the stage.
Once there, Luigi must start climbing the vines, however, he must wait – and take on the chin – an incoming projectile from one of the Hammer Bros. Upon being hit, once player one resumes control of Mario, the beanstalk from World 5-2 will start growing in World 1-2, providing all you need to infinitely kick shells for unlimited bonuses.
While watching the video may send you into a dreamy nostalgia trip, we recommend preserving your sanity by watching it on mute after the first three minutes – unless infinite life sound loops are part of the nostalgia kick.