A Boo Block is an enemy in the Yoshi series debuting in Yoshi's Story. They are a combination of a Boo and a block with pink and white stripes.
Yoshi's Story[]
Boo Block first appears in Yoshi's Story. They are only found in the level Ghost Castle where they disguise themselves as a block until Yoshi or your Yoshi is looking away where they take the appearance of a Boo.