Doomguard: The Doomguard serve as the Burning Legion’s lieutenants, captains, and generals. While it is incredibly unlikely that a demon hunter would be capable of defeating a Doomguard within their summoning circle, those that succeed would be granted overwhelming and overbearing power, the like that few would be able to contain. However, just as the Doomguard serve as the Burning Legion’s battlefield leadership, perhaps a sliver of that might be imbued within the handful of demon hunters capable of binding themselves with one and surviving.
Within the context of Classic, the method most frequently proposed is to re-tune bosses to make them harder. Rather than copying the numbers, re-create the relative difficulty. Kind of like, when you first start working out, you use small weights. When you get stronger, you lift bigger weights. The WoW community is more knowledgeable, more experienced, has better hardware, etc. We're "stronger." So give us tougher bosses. There are a lot of forms that could take. Bosses were constantly re-tuned during vanilla anyway, so if Ragnaros does 10% more damage or something, is that really a problem? I don't think it is. What about resistance gear? back in the day, collecting resist gear was a thing people did. But the numbers and strategies are so well known today that only the tank really needs it anymore. Bosses could be re-tuned with more resistible elemental damage so that's important for entire raids to gear appropriately. That would be entirely keeping with the spirit of vanilla even if the actually numbers sitting in a database somewhere were different than they were ~13 years ago. If you want to go a little farther, a few people have proposed adding new abilities to old bosses, adjusting their timing, etc.
In player vs. player designated zones, you will still be viewable and attackable by players, but you are not left completely defenseless. While engaged in a Pet Battle, any attack from another player will break you out of the battle. You will receive a 3 second damage shield that will absorb 50% of incoming attacks. The same exact wild pet that you were previously battling will respawn after you come out of combat with the other player. However, if you defeated the primary pet in battle prior to leaving the match, the pet and its team will not respawn.
Succubus: In the same vein as the imp avoids harm, the succubus is known for slipping in and out of sight on the battlefields, attacking when least expected, and relishing in the pain delivered to their opponents. In the same vein, both pain and pleasure enact a power to the succubus. To the demon hunter bound to a succubus, this might showcase itself with a particular knack for invisibility spells, turning pain into power, and even an affinity with the use of charm spells.
I used Zygor for legion and BFA, used AA on an alt for BFA. Personally i like Zygors format more. I like being able to target things like achievements. I used Zygor to get my Mindworm and my Lucid Nightmare as well as finish the Rep grinds for the allied races. I have zero complaints. My experience was great. I also used Zygor for some professions, recipe acquisition, a couple mounts, all of the Suramar quest line. Thank God for that. And for the last zone of Draenor on my Demon Hunter.. i forget the name.. Whatever the big daily hub thing was called.