There's going to be the inevitable question of "why not just edit the notepad file?" The reason is simple: that doesn't work, and when trying to play the map, if the negative BPM is the only timing point, the map won't load at all (or rather, it will infinitely try and load the map). Upon loading this up in the editor, the reason becomes apparent, where if you try and test it, osu! is recognizing the map as not having any timing points, despite very clearly having a timing point. If you try and input a negative SV (well in notepad, SV changes are denoted as negative values anyways, so trying to turn it positive by either removing the negative or adding a second negative), the game recognizes this as a positive SV still.
This means a negative BPM in a song with varying BPM is our only hope of anything. Unfortunately, nothing really happens here, although interestingly enough, doing this on a ranked map makes osu! still consider it ranked. Still, trying to play it yields the same results as when you tried to load the map with a negative BPM: it will infinitely try and load the map. What's worse about these situations is that you cannot hit your exit song button, as it no longer works. You're forced to ctrl+alt+del or alt+F4 or however you forcefully close the game (there are varying methods to this too). However, this will also happen when you try and test the map in the editor, as you do have a valid timing point, and that's all osu! checks for when it comes to opening a map in the test mode.
So yeah, any negative BPM does not work. However, a BPM of "0" does work. Why do I put "0" in quotations? Simply put, it's actually impossible to get a BPM of 0 in osu! The BPM found when looking at a song from the song select doesn't support digits, so anything below 0.5 will be displayed as 0, but the editor does. Firce777 in their map had made the seemingly 0BPM sections actually 0.01BPM, or more accurately, 0.6BPH (0.6 beat per hour). However, you can actually go lower than this. In the notepad file, timing points (not SV changes) are denoted for the sake of simplicity, as the opposite of what you see in the editor. This means in the notepad file, the bigger the number, the slower the BPM is, and the smaller the number, the faster the BPM is. So knowing this, what happens if you put the lowest positive number, a zero, into the notepad? Well, unfortunately, it's the same result as the negative BPM, except noticeably choppier, possibly because osu! is trying to comprehend what essentially is +infinity BPM.
So if we can't input 0, we can approach 0, right? The answer is yes, though with some...interesting effects. The drum mascot will stay frozen in animation due to how fast the BPM is (at 0.1, the BPM is 600000), and the line markers...
https://osu.ppy.sh/ss/6375145. You'd normally see multiple line markers when the song is scrolling exceedingly slow, but because the song is scrolling so fast, you physically cannot see how fast they move, thus resulting in this. The game might not see it either. Also in the editor, if your tick-mark rate is high, the editor will chug due to how many tick-marks are on the screen at that moment. Of course, if you had an ultra-high SV, the same effect would be achieved, but without the chugging. If the SV is set to 0...it gets treated as 1. If the SV approaches 0...also rather anti-climactic, where it gets treated as 8, even if it displays itself as larger (over 1mil as an example), possibly again a limitation of the editor.
Regarding all of this, how did MinG get his map to have -infinityBPM? After all, entering a super high number by itself doesn't do anything except give you +infinityBPM, and we've already discussed that -BPM doesn't work. The only thing I can think of is that once again, this is a fault of osu!, where it doesn't know what to think of -infinity, and just runs the game anyways. This is just pure speculation though, I have no idea what's going on with -infinity.
tl;dr again, negative or 0BPM with the exception of -infinity will give an infinite loop of loading, negative SV gets treated as positive, and 0SV gets treated as 1SV. BPM and SV are allowed values approaching 0, and while BPM can approach and even reach infinity, SV gets locked at 8 no matter how high the value is.
