Nintendo has some of the best producers, I swear by it. Sitting with Yoshiyaku Koizumi, he was part of a sit-down interview where he was asked about Odyssey, and why some levels have coins in unexpected places. The reason is simple, because the QA testers got to unexpected places, so the developers honored them by placing coins there.
Koizumi also touches upon Mario’s nipples and whether Toad is wearing a hat or not, he says it’s part of his body and not a hat – I’m on the fence about all of this. The video is short but well worth checking out if you want to hear some fun stories about the development of Super Mario Odyssey.