I'm trying to figure out how long it takes to break one piece of obsidian with my fist with Mining Fatigue 255. How long does it take? How about underwater? With a pickaxe?
I know that Mining obsidian with my fist takes 250 seconds or 4 minutes 10 seconds (9.4 seconds with a diamond pickaxe). Divide it by 0.27% (source: Minecraft Fandom) and I can break one piece of obsidian with my fist for 25 hours 43 minutes and 13 seconds with standard Elder Guardian Mining Fatigue III (3481 seconds, or 58 minutes 1 second with a diamond pickaxe). Now let's find out how long it takes to break obsidian with Mining Fatigue 255. I can't really find the percentage, but I found a video that gives an idea of what it's like to have Mining Fatigue 255 (giving credit to kooldude1008)
Here is a chart from Minecraft Fandom where it takes this long on breaking a block with Mining Fatigue:
I found the pattern using a graphing calculator: We divide the Mining Speed by 3.3333 for every level of Mining Fatigue we apply to the player. Dividing each level by 3.3333 (which took about 5 minutes) until level 255, the answer is 1.01337 × 10^-135% Mining Speed. Breaking it down, it will take 2.46701 × 10^139 seconds to break one piece of obsidian with my fist with the highest level (255) of Mining Fatigue. It's such a large number that it's hard to break it down to a smaller number for the number of years it takes to do the job. Breaking one piece of obsidian with a diamond pickaxe with this large effect takes 9.27597 × 10^137. Again, too long for a person to live. (I will add a table below for the times for other methods of breaking obsidian.)
Breaking a block of any kind takes 5x longer than it is to break the block out of water. If I'm floating in the water and my feet are not touching the ground, make it 25x instead of 5x.
In other words, I basically cannot break blocks with Mining Fatigue 255.
Here is a chart for the breaking times for obsidian (TI-nspire CX II CAS): (Other tools are excluded to avoid spamming)