The best way to do this to cater to everyone would be to add an item that is given to the player on world gen or that can be crafted with just some wood that activates the hard mobs/bosses. Then on servers admins. Could simply ban the item and cheat it in when their server is ready.So you're essentially asking for harder mobs or a progression based mod like a quest type mod? I agree. There should definitely be some high tier mob besides the Wither (can kill that in 3-6 blows, I forgot) or the Ender Dragon (just annoying). The problem is that mods tend to use vanilla Minecraft as a "baseline." After all, you have to cater for those people that use just vanilla MC with their choice mods added. The thing is, the mod we have in mind will need more than just enchanted diamond armor which goes beyond the vanilla MC baseline.
What I'm trying to get at is that a mod maker has to take other mods like Modular Power Suits or the KAMI armor into consideration when making the super hard mob. Once that happens, there'll be a "reason" for having the super powered gear as we'll use it to defeat the boss. Or have boss mobs that come around once in a while that increase in difficulty with play time so that there's a reason to continue to get super powered gear.
But now the problem is that there are those players who build slowly or like to completely finish a mod before moving on, and they might lag behind the mob mod and find that they're not ready in time and continuously die / lose stuff (as the mobs from the mod should destroy things). So you have to have people ready for the mod, but also cater for the people who like to grab the armor first.
So as a result, whatever direction you go, you'll be catering for a very small group of people out of the modded minecraft community, which brings up the question of whether or not it's worth it to maintain such a mod.
Just my 2 cents.
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