Wallop

Wallops are a species of Whomp introduced in Super Mario 3D Land. They look like Whomps, except they are shaped like a fort wall with black eyes and yellow pupils, with mouths and feet. Instead of attempting to squash Mario and Luigi by slamming on the ground when they get too close, Wallops block Mario/Luigi's way by walking sideways to stop them from passing by it, similar to Whomps. If Mario and Luigi jump, the Wallops jump too, which is something Whomps are not capable of doing.

Super Mario 3D Land
Wallops make their first appearance in Super Mario 3D Land, where they are found in many places of various themes. They block Mario's way, walking in front of him and taking the same directions Mario goes, stopping him from getting past it. Wallops can also jump whenever Mario jumps and then slam the ground. After jumping, there will be a few seconds in which the Wallop will recover, giving Mario or Luigi a chance to pass by it. When the player is a certain distance away from or behind a Wallop, they will be in a state of dormancy, in which their pupils are no longer lit and their feet have retreated into their bodies, until the player is in front of them. Mario or Luigi can destroy them by standing below them when they jump as Statue Mario or Statue Luigi, or turning into a statue above them. They make their first appearance in World 3-1; they also appear in World 6-4, World 8-6, Special 3-5, Special 6-1, Special 8-4, and Special 8-Crown.

Super Mario 3D World
Although Wallops don't appear in Super Mario 3D World, a sub-species called Walleyes act similar by moving side to side continuously to block Mario's way. Walleyes are the same as Wallops, except they have bigger heads with spikes on the top and hands which the Wallops lack, besides different eyes. Unlike Wallops, Walleyes can be stunned by Mario's attacks (such as being scratched as Cat Mario or whipped by Tanooki Mario), giving Mario (or Luigi, Peach, Toad and Rosalina) a chance to get by the Walleye before it recovers.

Trivia

 * Wallops' mouths are identical to those of Rhomps.
 * Wallops are very similar to Blocky from the Kirby series.
 * Like Whomps, Wallops seem to be inspired by the Japanese, mythological creature nurikabe. Nurikabes block the path of travelers, just like Wallops do.
 * The name Wallop is also a pun on "wall", due to how they look and behave like walls all the time, and the term, "wallop", which means to make a loud crushing noise, or a large attack or beating.
 * By running into a direction and immediately turning the other way, Mario or Luigi can get past the Wallop without jumping.