At the end of Metroid II: Return of Samus, there is but one Metroid left in the universe. Bad things happen, and Samus Aran must once again head for Planet Zebes to battle Mother Brain, Ridley, and the Space Pirates. (And a few other bosses too.)
This movie improves on both prior low% runs (one that collects the Ice Beam and one that collects the Speed Booster) by collecting the Speed Booster and using various Shinespark-related glitches to render the Gravity Suit unnecessary, pushing the total required number of items from 14 down to 13. The author's comments are very detailed, and well worth a read if you're curious about just how everything was done.
There are a number of other routes that can be taken while still getting 13 items, but all of those routes require a specific glitch when fighting Draygon which gives you a non-infinite but arbitrarily large amount of ammunition; the item route in this movie does not permit the use of this glitch. If you would like to see this glitch, it is featured in the following (now-obsoleted) iteration of the any% run.