Do you know Azuregos or Lord Kazzak of the Vanilla Version of World of Warcraft? They were outside of instances and gave you a debuff after you died...your were unable to get into the fight for 10 Minutes after your death. (Or you were permanently frozen or one shot again)
I was editing my post while you quoted it (revoked the changes, since you already had quoted).
This is some of what i had added
If a fight is not instanced, people can simply respawn and return to battle as often as they like (unless dying causes a significant, stacking malus for a limited time and/or respawn has a significant delay), or new players come and join in.
Many people in one area do not act as a coordinated group, where every single player matters, but as a mob, where nobody really matters and where no tactics are applied.
The higher the number of players, participating in the same event, the lower the importance and the impact of the individual (unless something like a tank class exists, because in that case, it would be the opposite, for that specific player).
If an enemy does not scale with the number of players, it becomes easier with more players.
If an enemy does scale with the number of players, those who are skilled get indirectly grieved by those who are not skilled.
If players can respawn as often as they like, any enemy will die at some point.
If players get a malus for respawning, it should be completely incapacitate them for a significant amount of time (like what the old WoW bosses caused).
These world bosses needed some coordination of tanking, healing, not attacking after certain abilities (aggro wipe), not wasting mana and more.
They became weak when new items and instances were introduced but at first they were damn hard to beat, even with new players joining the fight.
I am all for bosses with such abilities, however:
According to MK, EVERY "class" is supposed to be optional in Ember.
There is supposed to be no content at all, where anyone is forced to play a specific role, so no requirement for tank or heal (which i find pretty bad, to be honest).
I don't know how well it worked back then, in WoW, but i know that if you now tried to do any kind of open world fight where any kind of tactics have to be applied, there would always be a number of people who are such special snowflakes, that no rules apply to them.
They will do what ever they like, no matter if it wipes out 100s of players or not.
People will deliberately sabotage fights, if they can.
Just look at many people in these forums.
They do not want any kind of teamplay.
They do not want to have to follow any kind of instructions/rules.
If the individual matters, there will be people who grieve the shit out of the community.
If the individual does not matter, it is not about skill anymore.
Back in WoW, the community would punish assholes and they would have to suffer from not being invited into raids/groups (which were necessary to be able to play most of the game).
If there is only open world content (where groups are not important), that does not work.
If there is no retaliation for people being scum, they will behave as they like.
If isolation has no negative effect, assholes will show their true self.
Just look around the forums and see how many people are against any kind of requirements or bonuses for joining groups/guilds.
Probably there is a way to balance open world bosses for a game like Ember.
But it will be complicated.