Diagram of the hammer brothers in Super Mario Bros. 3, World 2.
https://files.mastodon.social/media_attachments/files/110/618/074/275/971/990/original/92fd95fc6936dab9.png
If this video confuses/bores you: Read this post then jump to 10:19.
In warpless SMB3 runs, there's an early (second world) instance of randomness where a hammer brother can run either right or left, and if it runs left you can skip three entire levels and save an entire minute:
https://smb3.bf0.org/smb3mechanics/2018-08-22-early-hammer/
Getting this randomness is important, so players use a "manipulation"– they play in a very precise way (in Mitch's case, literally miming along to a video of a TAS) to get exact random numbers.
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