You are allowed to use MS Paint. "External tools" means things like the Witness Trainer or Autohotkey.

It's a meme in the Discord server. A developer-accepted name for the waterfall cave is the "Benis Cave".

That's actually an intentional feature of the autosplitter. It's to avoid people using the autosplitter to figure out whether they solved the snipe correctly. If you look in the autosplitter settings, there's an option that says "Unsplit when restarting a long-distance puzzle". If you check that, then it will automatically unsplit when you re-attempt a snipe and it'll properly split again when you're done with it.

There are no rules on the leaderboard, but the debug console should probably be banned. The FixedEngineFPS setting speeds up the game if set to a low value. I used "set FixedEngineFPS 200" (low enough that it doubles my speed, but not too low that I can't double jump) and I beat it in 3:48.