Necessary for 0%.

Skipping BOB, or the thought-to-be-mandatory missile tank in sector 3 before the BOX fight, can be done in two ways.

There's the old fashioned way, storing a speedboost and making it all the way up to the vine that can be shinesparked through. Only has a few frames of leeway and you probably needs to pause buffer a million times to have a decent shot at it (video by Biospark):

Alternatively, there's the much easier way to do it now, discovered by ZX497 in 2016, that involves briefly going out of bounds. Can be seen here:

Keep in mind that the out of bounds skip is ONLY possible on the US and EU versions (even the re-releases), but cannot be done on any Japanese version of the game (and probably not on the iQue version either, since it seems to be based on the JPN version).

Be sure to follow the video description exactly for the latter skip.