Stalking Piranha Plant

Stalking Piranha Plants are sub-species of Piranha Plants that appear 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. These enemies can be defeated by a fireball, being frozen, hit with a Starman, or being hit by a shell.

The Piranha Plants in Mario Party 3 also have legs, which might have been the inspiration for this.