I suggest that you add an area that allows for a custom encounter with Extreme/Savage Content. It would be an "holo deck" of sorts(I know you couldn't call it this). This would be accessible through the FC housing. You may want to add holo tapes that are needed to be collected in order to unlock an encounter. these would drop from doing either the extreme/savage or the normal mode of the same version.

The "holo deck" would allow you to see the area w/o the boss. Later you could add the boss. But, it can't do damage to players and mark them instead if they get hit by an avoidable mechanic. And have it where you can place the Boss in a certain "Phase" of each battle.

I believe that implementing this feature would allow people to strategize how they are going to defeat a boss. Putting it in FC housing would limit the amount of people who could use this feature at once and add more of an importance to be in an FC.