Super Mario Bros. Forum  /  Theory for potential timesave in Famicom version
  RoseNoArsonRoseNoArson

There is a well-known bug in the Famicom version of this game allowing the player to reach levels such as World K-1 by switching quickly to Tennis, doing things to set memory slots, and switching back to Super Mario Bros. I theorize that there might be a way to use this to warp to 8-4 very early. Further study is definitely required, but this might save minutes in the Any% run. The question is whether this is allowed as it involves switching to Tennis to work. Is switching games midrun like that allowed?

 
  WolfAeterniWolfAeterni

We theorized this route a couple months ago. We understand how it works, but no one was able to test anything 'cause we didn't have a famicom/top loader. You can't warp to 8-4, only 8-1, which would save about a minute and a half if we consider the time spent doing the cartridge swap. Also, not, this is of course not allowed on the leaderboards lol