"Some bosses receive reduced damage from ranged and magic damage increasing the priority of melee classes and Devo." This would need to be done carefully since melee classes damage is already very competitive with ranged and magic classes. Instead of this I'd just say that you put ads in the fight that require a dedicated tank, which in turn will make people use more devos which will naturally make melee classes played more
"Multiple bosses in an instance where one takes reduced damage from ranged, one takes reduced damage from magic, and one takes reduced damage from melee. "
This sounds fine, but boring as a mechanic. It feels like forced party diversity but at the same time, it works well. Maybe make it so that while the boss is weak to one of the three, there are mechanics/ads that are doable by the other two types of damage so that they have something to do
"Bosses take increased damage based on the number of players hitting it. The focus on # of players hitting it makes it so that people can't just bring afk players. The scaling could have a cap of 7 players, so that support classes will be involved. Alternatively, a similar mechanic with boss self-healing. "
Just add a lower party limit like max 8 players instead. This suggestion has the unintended effect of making people just duo content since it's easier and it's more rewarding the less people you bring anyway.
"Bosses constantly summon difficult mobs. "
That's standard pratice yes. Although I don't think I've ever seen anyone saying that infinite ads are "fun"
"Similarly, bosses summon waves of mobs and take less damage based on the percentage of the mob still up.
This is good
"Bosses switch between Ranged Damage nullification, Melee Damage nullification, and Magic Damage nullification."
This one is a tough one. While I can see it working, all I think it'll do is make for a confusing mechanic that throws things out of wack if not done properly. I'd rather have multiple bosses like was suggested before than having this.
These are really good suggestions Choi 😃