Boo Buddy Snake
From the Super Mario Wiki
A Boo Buddy Snake is an enemy appearing only in Super Mario World. It is composed of six to seven Boos that bounce and rebound diagonally off walls and ceilings, making it a very dangerous obstacle for Mario and Luigi. Although usually harmful to touch from any side, it is possible to rebound off a Boo Buddy Snake safely by Spin Jumping on the frontmost Boo in the line.
Another similar Boo formation is the Circling Boo Buddies.
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