I'm on Yog-Dzewa, the final boss of pixel dungeon. I was dealing damage to Yog-Dzewa (the eyeball) just fine, but now I am not. I know that the fists each contribute a damage divisor of 2 so I destroyed both of them (and all the larva, just to be safe) and I am still dealing 0 damage on every hit. The wiki claims Yog-Dzewa has 0 armor, so I don't understand why this is happening.
This is due to a major bug. This bug exists on all versions at least through 1.9.2a.
If you quit and reload during a fight with Yog-Dzewa before killing the fists, you need to kill and restart the app or you will deal no damage. Each time you load, the app adds the current number of fists to Yog-Dzewa's damage divisor without resetting it from the last load. Even one reload will put you at a fist count of 4, meaning a damage divisor of 16, meaning you will deal almost no damage. Killing and restarting the app will fix this if you reload by accident.
I have added this note to the wiki page on Yog-Dzewa as well