Havoc in Battle for Azeroth has gone through somewhat of a maturing process, trying to focus more on the talent tree and allowing for more diverse options in gameplay approaches, alongside tightening up some of the more loose aspects of the original implementation. It still remains a predominantly builder spender style rotation and is largely Global Cooldown locked. The core hook is making the most of your Fury pool and reacting to unpredictable gains, ensuring you use high burst cooldowns and windows to push yourself even further. On top of that, it comes with a variety of mobility and defense tools, creating a versatile toolkit with some unique abilities that can be used in a variety of ways.
The prepatch for Legion, for example, offered players in-game demon invasions throughout the world of Azeroth, presenting opportunities for new appearances, feats of strength, a pet, a toy, gear that provided a catch up in power for those with alternate characters or who hadn't played in a while and the opportunity to infect other players via an in-game mechanic.