I have not played much of any 21st century video or computer games but I suppose it still applies just the same. One of my favourite games as a kid was Mortal Kombat II (SNES port and occasionally PC) and me and my friends (mostly me) would toy around with the buttons within that four or so second time period hoping to discover a new fatality.
I remember coming up with two fatalities on my own. One was Mileena’s fatality where she swallows the opponent whole and spits out the bones. I just randomly smashed buttons with the block on and would repeat it. I remember it was either summer or autumn and I was playing as Baraka in the pit level, leaped over the opponent while hitting either the left or the right button of the pad (depending on direction of the jump) and hit Y and I got it; the opponent’s head took off. I believe I then proceeded to go to my grandmother’s place for dinner.
Memories are ambiguous but I might have also crossed Kitana’s decapitation fatality, Mileena’s friendship and perhaps Rayden’s uppercut fatality, though in the latter case it would have been a friend’s invention.
In MK3, I might have accidentally discovered Stryker’s electrocution fatality. It is the only reasonably doable move in the absence of cheating so that may be why I have such a potentially false memory.
The cartridge package came with a paper instructing me to send some stamps to a specified address in exchange for a complete fatality/secrets manual, which I received several weeks, possibly months later.