I love the story behind the Adventure easter egg, game designers deciding that if they couldn't get credited for their work they'd do it for themselves

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Isn't there an easter egg in Halo (might be only the later platnum/classic version?) where if you walk out into the ocean at one point you can find an island and statue advertising Halo2.
NBA Jam's (arcade version from early 90's-ish) big head mode.
I'm not sure if anyone else was told or if it was on the arcade games elsewhere but when the original Street Fighter was in a local deli there was no mention of Ryu's fireball (which I think was the only special move) and seeing as the joystick quarter-circle wasn't in every fight game at the time no one knew why every now and again your little karate guy would stop to thow a fireball out of his hands! I remember seeing SF years later, after SF2 was out and just had to play a game to prove to myself that it was the same move

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I remember when FF7 was out there were so many rumours about hidden easter eggs many relating to what glorious event would happen if you gave up on life and raised 100 golden chocobos.