Brier

Briers are floating creatures that are covered in spikes. They only appear in Yoshi Touch & Go. Briers are common enemies in this game, and they are in almost every level. Shooting eggs is the only way to defeat them, as they pop bubbles that are drawn on them. Briers continually pulse their thorns in and out; hitting them while their thorns are retracted allows the egg used to go through them while hitting them while their thorns are extended destroys both the egg and the Brier. There are two varieties of Brier: the normal, green variety and the red variety; the only difference between these varieties is that they each pulse their thorns at opposite intervals. Additionally, there is a variant called a Marucchi that can be encased in a bubble.

In Balloon Trip, the tech demo Yoshi Touch & Go was largely based on, the design and palette of Briers seemed to indicate that they were actually the Urchins of Super Mario World. These Urchin-like Briers were only seen in one standard variety. Super Smash Bros. Brawl features a Brier sticker.

Yoshi Touch & Go
(It does not move from its position, but moves its spikes in and out. If you hit it with an egg when the spikes are retracted, it will penetrate the spikes. On an empty course, you will not be able to defeat it unless you take a super start. Dodge the spikes as you go.)
 * Shogakukan guide: その場から動かず、トゲを出したり引っこめたりする. トゲが引っこんだときにタマゴを当てると貫通する. 空のコースでは、スーパースタ一を取らない限り倒せない. よけて進むこと.