World 8-4 (New Super Mario Bros.)
From the Super Mario Wiki
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This level is a more standard overworld level, and features Scuttlebugs repeatedly dropping down from the top of the screen and trying to chase after the player.
The level begins with a pair of Scuttlebugs dropping down as soon as the player starts moving. More and more Scuttlebugs drop down as the player progresses through the level, often grouping up tightly; the player must be quick going through this level in order to avoid being overwhelmed. The player will then come across a section of moving platforms above a bottomless pit, with the Scuttlebugs making jumping between them difficult. After this, the level's checkpoint is reached.
After the checkpoint, the Scuttlebugs drop down in higher numbers, making the rest of the level harder. There are more moving platforms, most of them moving horizontally, making for hazardous platforming. The player will eventually come across a ? Block containing a Super Star, which can be used to score multiple 1-UPs thanks to the numerous Scuttlebugs. After more moving platforms, the flagpole will be reached, guarded by one final Scuttlebug hanging down from a web.