Goombas, the walking Shiitake mushrooms, was created at the very end of Super Mario Bros. development

A portion of an Iwata Asks: Vol. 2 interview with Iwata-san, Tezuka-san and Nakago-san…

Tezuka: We came up with all kinds of objects, all the time trying to limit the bytes we were using. Then right at the very end, we made the Goomba.

Iwata: You’re kidding! You made the Goomba last? (laughs)

Tezuka: We did. Even though it’s now such a major part of the game, at the beginning we actually only had Koopa Troopas. Then when we got people to play the game, they would say that it was quite tricky to encounter Koopa Troopas at the very start.

Iwata: Right, because defeating a Koopa Troopa is a two-step process.

Tezuka: So we decided that that we should make an enemy that you could easily squash with a single blow. That’s why we made it so that the first enemy the player would encounter would be a Goomba. But we created it right at the very end.

Nakago: But by the time we had decided we were going to make the Goomba, we had hardly any bytes remaining.

Tezuka: And as it was an enemy, the character needed to have movements.

Nakago: That’s why by having it rotating from left to right, we made something that looked like it was walking. That’s why the Goomba’s body slopes slightly.

Iwata: I see. So you’ve doubled up a single image.

Nakago: By doing this, it looks like it’s trotting along.

Iwata: By the way, is it a coincidence that the Goomba looks like a mushroom?

Tezuka: It’s a shiitake mushroom!

Iwata: It’s a shiitake? (laughs) So it’s not a chestnut?

Tezuka: That’s right. (laughs)

Iwata: But leaving that aside… (in a serious tone) The Goomba was really the last thing you made?

Tezuka: (laughs)

Iwata: That’s really come as quite a shock to me! This is another thing I had no idea about! (laughs)