An officially licensed bottle of Mario shampoo from Japan with an attached waterproof picture book contains a small unique illustration showing that the book can be read while bathing, using Yoshi as a subject. Below is the illustration, upscaled and isolated.
In Yoshi's Island, if the "Kamek saying 'OH, MY!!!'" object is inserted anywhere in a level that is not a boss battle, Baby Mario will explode. This will count as completing the level.
Unused image found in the data of Yoshi's Story. Note that Baby Mario does not appear in the actual game; as it was known as "Yoshi's Island 64" during early development, it is possible that his inclusion was at some point considered.
@RockerYoshi Hi, I'm the original artist of this image. If you're going to post it, please remove this tweet and credit me next time.
Also, it's not even Yoshi Day, that's on 4/4!