When a lot of games had cheats? Not cheats like, a mod or some kind of crap like that, but actual passcodes you could enter in for some bonus content? If you played games in the 90's, damn right you remember.
I recently stumbled upon this site, a site I used when I was ten or so, thought it was pretty nostalgic.
Then I remembered something else. Funny story actually. I used to be big into the Original Smash Bros, and according to this site, I hadn't unlocked all the characters as I thought (Protip: They don't exist.)
You see that? It says Spiderman, Metal Mario and Venasaur. Man, when you were 10, you didn't question that, you just thought "Oh shit, I wanna unlock that. So I actually tried getting all those characters, not Metal Mario of course, but I attempted for Spiderman and Venasaur. As you can see, the requirements to unlock them are batshit insane, and as a kid, I tried the Spiderman one at least 5 times.
Remember kids, never trust firstname.lastname@example.org