What is the rarest thing you can fish in Minecraft?

Please look at this from a mathematical perspective. If you did, include math and sources. I will be using some data from here for a project.


Solution 1:

There is a 0.9% chance of catching 10 ink sacs in a jungle biome, the rarest catch in the game. The second rarest is 1% for 10 ink sacs in a normal fishing environment. There's not really "math" to get that number besides understanding weights, which is just a natural number telling how common drop should be.