How did those hidden power-ups in Super Mario actually work?

As much as I love retro games, there are a host of aspects of the 16-bit era I'm more than happy to leave in the past. The mind-numbing tedium of having to replay a game from the beginning every time you lost felt like a leisure activity designed for Gitmo detainees. The only upside to playing a level ad-nauseam was the insane mastery you'd accrue after a thousand runs. If you plucked me out of a coma, I'd still be able to finish the first three levels of Spider-Man: Maximum Carnage without losing a single life. When the Alzheimers sets in and my kids tearfully mourn my memory, I'll still be able to scoop up all of Venom's hidden power-ups through muscle memory alone. 

In the video linked above, the YouTube channel Kosmic explains which power-up in Super Mario Bros. is the most concealed character boost in the game and how you can consistently acquire it.