Big Wiggler

Mega Wigglers are a sub-species of Wigglers that first appeared in New Super Mario Bros. Wii. They are five times the size of a normal Wiggler (but they're not bigger than the Super Mario Sunshine's Wiggler) and live beneath the ground in places where it has acid pits.

New Super Mario Bros. Wii
In New Super Mario Bros. Wii, despite being enemies, they can help Mario get the items in places of high range. For this, the player must jump over a Mega Wiggler and press the button 2 or A to do a high jump, as if he were using a Spring.

Mega Wigglers cannot be defeated and they'll hurt Mario by running into him. They can also defeat Swoopers. Also, they don't get angry if Mario jumps atop it.

Super Mario Galaxy 2
They reappear in Super Mario Galaxy 2 in the Supermassive Galaxy. They appear on the Stone Tube Planet and Mario must avoid them to reach the Power star. Nothing can defeat these foes and like most giant enemies, they hurt Mario if he touches them. The Co-Star Luma will be able to stop them from moving and hurting Mario.

Trivia

 * Mega Wigglers were originally going to appear in New Super Mario Bros.. However, a gigantic one appeared in World 7-3.
 * Through hacking methods, it is possible for Yoshi to eat a Mega Wiggler in New Super Mario Bros. Wii. This is the only way to defeat a Mega Wiggler in that game.