Stalking Piranha Plant

Stalking Piranha Plants are a type of Piranha Plant that appear in the Mario franchise as enemies that often have the ability to stretch their necks and walk around. They are similar to Elasto-Piranhas from Mario & Luigi: Partners in Time, but with a design closer to Ptooie from Super Mario Bros. 3.

New Super Mario Bros. Wii
Stalking Piranha Plants first appear in New Super Mario Bros. Wii, where they appear in World 5-1, World 6-3, and the World 5 Enemy Course. When the player(s) is/are not nearby, they walk around on two legs, like Ptooies, and when the player(s) approach(es) them, they stretch out their necks up and downwards in order to block the player's/players' paths and to attack them. These enemies can be defeated by a fireball, a Star, or a shell, or by being ground-pounded when frozen by an iceball. Like most Piranha Plants, these enemies cannot be picked up when frozen.

New Super Mario Bros. U / New Super Luigi U / New Super Mario Bros. U Deluxe
Stalking Piranha Plants reappear in New Super Mario Bros. U, New Super Luigi U and their Nintendo Switch ports where they act the same as they did in New Super Mario Bros. Wii. They appear as rare enemies in Bramball Woods and are much more common in Walking Piranha Plants! and Rising Piranhas.

Yoshi's Woolly World / Poochy & Yoshi's Woolly World
Stalking Piranha Plants reappear in Yoshi's Woolly World and in its 3DS port, being made of yarn and ribbon. They mainly appear in the level Naval Piranha's Sewer. In this game, if the stalk of the plant is hit, then the head will fall down next to the body, and the two will rejoin each other shortly after. When the head and body rejoin, a sound plays similar to that of a Dry Bones' regeneration sound. Attacking the head will permanently defeat the Stalking Piranha Plant. They attack similarly to how they attack in New Super Mario Bros. Wii.

Mario & Luigi: Superstar Saga + Bowser's Minions
While Stalking Piranha Plants do not appear in Mario & Luigi: Superstar Saga + Bowser's Minions, a new variant of Stalking Piranha Plants known as Fire Stalking Piranha Plants appear in the Minion Quest: The Search for Bowser mode.

Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey
Fire Stalking Piranha Plants reappear in the Bowser Jr.'s Journey mode in Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey.

Super Smash Bros. Ultimate
In Super Smash Bros. Ultimate, Piranha Plant has an attack where it stretches its stem to bite distanced opponents, which is based off of Stalking Piranha Plants and Elasto-Piranhas. On Palutena's Temple, Stalking Piranha Plants (just called Stalking Piranhas) are mentioned briefly by Viridi during Palutena's Guidance dialogue for Piranha Plant.

Trivia

 * In various official social media posts, Nintendo consistently mistake the Ptooies in the course in Mario Kart 8 Deluxe for Stalking Piranha Plants.