Unibo

Unibō are nearly indestructible spiky round enemies that inhabit flying and swimming areas. They appear in the Hippo stage and the second level of the Turtle Zone in Super Mario Land 2: 6 Golden Coins, where they can only be defeated by a Star or Koopa Troopa shell. They remain stationary until Mario comes near, at which point they will shake on the spot to make themselves harder to avoid. They reappear in Mario & Wario, redesigned to look more like Urchins and with no visible eyes. In addition, they come in two varieties: those with blue bodies move vertically, and those with yellow bodies move horizontally. They no longer sleep and are constantly moving around.

The original appearance of Unibō is very similar to both Gordo from the Kirby series and Sea Urchins from The Legend of Zelda series.

Perfect Edition of the Great Mario Character Encyclopedia
「ウニボー 種族 アクア族 性格 しんぼう強い 登場ゲーム ランド2、M&W」 謎の物体それがウニボー ランド2では、海や宇宙で登場. 普段は空中でじっとているが、近づく突然動かが激しくなる. マリオとワリオでも、上下しているだけの謎の生き物. 避けりしがない.

Unibō Species: Aqua Tribe Disposition: Persevering Appears in: Land 2, M&W Unibō is a mysterious object ''In Land 2, they appear in the ocean and in space. Usually stays still in the air, but suddenly starts moving rapidly when approaching. In Mario & Wario, it is a mysterious creature that only moves up and down. There is no way to avoid it.''