Stalking Piranha Plant
From the Super Mario Wiki
Stalking Piranha Plants are type of Piranha Plant that first appears in New Super Mario Bros. Wii. They appear in World 5 as common enemies and World 6 as rare enemies. When Mario isn't around, they walk around on two legs, like Ptooies. When Mario approaches, however, they stretch out their necks to block Mario's path and to attack him. Stalking Piranha Plants also appear as the enemy of the World 5 Enemy Course. Outside the map are the Piranha Plants vines which can block areas and can only be moved by completing a stage. These enemies can be defeated by a fireball, ice-ball, Super Star, or a shell. Like most Piranha Plants, these enemies cannot be picked up when frozen.
Stalking Piranha Plants return in Yoshi's Woolly World, being made of yarn and ribbon.
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