Getting enemies / mushroom houses to reappear on the world map

On World 1 - Acorn Plains, there's a Piranha Plant that appears on the world map. He goes in and out of his pipe. If you beat him he disappears.
In the course of me playing the game I've observed that he eventually re-appears. But what are the specific conditions that need to be met for enemies on the world map to reappear? Do they reappear after x minutes? I beat a level just now and the Piranha Plant did not reappear. Maybe I need to beat multiple levels?
On that same note, do mushroom houses reappear after you've used them? FWIW I've beat The Final Battle in World 8 - Peach's Castle, and have three gold stars on the menu screen.
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How do I get my mushroom house back?
Beat the game to make all the Mushroom houses in Worlds 1-8 reappear. Collect ALL of the Star Coins (IN WORLDS 1-9) and visit/use every Warp Cannon to make the houses reappear and stay for good.How do you get the mushroom house in Super Mario Bros DS?
Stop the timer at 77,88 or 99 and you'll get a orange mushroom house which will award you with a mega mushroom.How do you get the white mushroom house in Super Mario Bros 3?
Secret Island is a small secluded area appearing in New Super Mario Bros. U, New Super Luigi U, and New Super Mario Bros. U Deluxe. It is situated between Acorn Plains and Sparkling Waters, and can only be accessed via the world map's Pipe Cannons after the game is completed.Super Mario 3D World - World Mushroom 100% (Nintendo Wii U Gameplay Walkthrough)
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