Hone

"これを取れば 変身できるんだな. がいこつになる だけですけど. (If you take this, you can transform. You just turn into a skeleton, though.)"

- Isshī

The Hone (骨, "bone") is a power-up that only appears in one chapter of Super Mario-kun volume 1 as one of the hypothetical items that would appear in a future game.

It is released by a skeletal Galoomba after being squashed. When Mario grabs it, it turns him into Skeleton Mario for three minutes.