How is this speedrun possible? The Legend of Zelda World Record Speedrun Explained

Watch the unedited run here:    • (27:57) The Legend of Zelda any% no up+a s...  
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Chapters:
00:00 - Introduction, layout, category
02:30 - Screen scroll, Level 3 manipulation
09:33 - Level 3
15:52 - Level 4, Item drop manipulation
23:25 - Level 1
29:40 - Level 2, Rupee route
33:45 - Level 5, Enemy movement, Recorder
44:55 - Level 7, World wrap, Roocorder
52:30 - Level 6
56:25 - Level 8
59:40 - Level 9, Conclusion

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