Tip: Test your levels as all forms of Mario (small, super, fire, cape). If it's possible to enter a level with Yoshi, make sure to test that as well.
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Important note: Since October 7th, 2018 the patches section has been ongoing a full fledged remoderation to convert patches to Asar and SA-1, as well as to do UberASM conversions of certain patches and some other quality control - further details here. If a patch you were searching for was removed, please check this thread to get a(n unconverted) backup.