"A wither skeleton has a 2.5% chance of dropping a wither skeleton skull when killed by a player or tamed wolf." So IIRC, you do 0.0250.0250.025 to get the chances of it and it basically is 0.000015625 (~0.0015625%)

Idk, the rules says "Save and quit is not allowed unless you encounter a bug that is only fixable by save and quitting."

Rules wouldn't make sense, you can literally spawn in water and, in most categories the timer starts when you start moving, so it doesn't make sense to add this category

I think you can optimize the time by choosing one of the first version of Minecraft, the world would generate faster 🤔

Could be fun to try