Always informative and surprising, the Iwata Asks series of articles is a treasure trove of Nintendo experience and and information, so you won't be surprised to hear that the latest article, covering Super Mario Galaxy 2, is chock-full of interesting facts.
Yoshi was originally planned for the first Super Mario Galaxy but was removed, as the team felt it would be too much for players. His inclusion in Galaxy 2 was one of the first things the team decided upon, and settled on his tongue-tugging action as one of the most important new gameplay features.
Far more ambitiously, the team also wanted to include switches that would drastically alter the appearance of the game's worlds, but this feature had to be removed as it proved extremely difficult to implement.
There are plenty more tasty crumbs of information in the article's first rough translation, and no doubt more will come when it's officially translated into English soon.