Boo Buddy Snake
From the Super Mario Wiki
A Boo Buddy Snake is an enemy 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.
A similar Boo formation is the Circling Boo Buddies.
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