Bossmode is the difficulty above Hardcore, which turns every single mob into a boss fight, even including passive mobs!
There are a lot of custom attacks, custom weapons, and custom armor that is unique for each mob. Some of the bosses are extremely powerful, so you need to use all the possible resources around you if you want to survive.
All Commands for general bossmode settings start with: BossMobs All Commands to spawn bosses start with: SummonBoss_
Can you beat Minecraft bossmode? Good luck.
Some of the bosses: https://www.youtube.com/watch?v=jbVklLPDjmE
