I attacked yi1 again in a different way which I thought of when I was in the bathroom.
http://dehacked.2y.net/microstorage.php/info/1038904130/smw-yi1test2.3.smv
This is like 41 frames faster in yi1 than
Masterjun's test. So we are now very close to the 10 minutes mark! I guess it's still improvable.
To understand this strategy, one should know first that a mushroom (or fireflower) from the reserved box is still active even when it's in the offscreen. So you need four reserved mushrooms to fill sprite slots #08-#11.
To do this you may think of the double-eat glitch. But the rule of the double-eat glitch is rather solid: for example, when double-eating a reserved mushroom (in #11), releasing a reserved mushroom between grabbing a mushroom (fisrt time) and swalloing (second time) gives nothing, because they are all in the same slot #11. But you can avoid this by using another sprite from a block: in the movie (around at frame 1400), a 1-up appears in slot #09 then a reserved mushroom appears in #08(!). After the 1-up mushroom is inactive, the reserved mushroom is duplicated. At this time, the latter reserved mushroom appears in #09 and the empty mushroom on the tongue is in #08, so no collision happens, meaning the mushroom #09 is never attracted to the tongue. Of course, in the case of the mushroom behind the grass, you don't need such a tricky process.
Anyway it looks so entertaining, doesn't it? ;)