From the Super Mario Wiki
Piranha Heights, or Acorn Plains-4, is the fourth level of Acorn Plains in New Super Luigi U. This level is unlocked by completing Rolling Yoshi Hills, and its own completion gives the player access to Lemmy's Lights-Out Castle.
The player begins the level on a Mushroom Platform above several Piranha Plants and a Big Piranha Plant on moving Mushroom Platforms. Mushroom Platforms that move up and down must be crossed, and a Big Piranha Plant and a ? Block are found. Three Piranha Plants are seen underneath a Warp Pipe. A Hidden Block containing a Super Acorn is found above the right side of the pipe. A stationary Mushroom Platform appears, with Piranha Plants on moving platforms below it. A ? Block containing either a Super Mushroom or an Ice Flower depending on the player's current form can be seen. Another Warp Pipe with Piranha Plants underneath it is found, above a Mushroom Platform with a Piranha Plant at the end. A Hidden Block containing a 1-Up Mushroom appears above the left side of the pipe. More moving Mushroom Platforms are found under Warp Pipes with Piranha Plants and a Big Piranha Plant underneath. After the last Mushroom Platform, the Goal Pole is found.
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