From the Super Mario Wiki
Itsunomanika Heihō is a rare type of Shy Guy appearing in Super Mario World 2: Yoshi's Island, Yoshi's Island: Super Mario Advance 3, and Yoshi's New Island. Itsunomanika Heihō appears as a normal Shy Guy and hides behind foreground objects, such as crystals; if a Yoshi runs through the hiding spot, a Bandit will appear and run off with Baby Mario, leaving the Itsunomanika Heihō in his place. This does not affect Yoshi himself in any way, and the Shy Guy can be knocked off and then defeated with any attack.
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