A powerful Super Mutant named the Green Terror has rallied a huge amount of Super Mutants, becoming a even greater threat than the Institute. Green Terror's forces began attacking the other super mutant groups, killing or forcing them to join. No settlement is safe from this great threat. The Sole Survivor's only chance to defeat this threat is to join up with a group of Brotherhood of Steel soldiers. Together you guys finally found the Green Terror's base but it seems him and all his super mutants are dead already.

Something even more dangerous has killed them. You and your Brotherhood squad are soon ambushed by a strange group of Raiders called the Death Skulls. Only you survived but you must make haste as you discovered their plans from a nearby terminal. They are planning on bombing Diamond City. The Sole Survivor rushes to the city and intercepts the death skulls just in time to stop them. Their leader has retreated up to the mayor's office and you must get up there and have a one on one duel with him.

Reward - A death skull mask with 15 def rating, 10 energy rating, and 0 rad rating.

Charisma - if high enough, you may convince him to jump down to his death.

Evil - You can join him and blow up diamond city so make sure you finish all your quests here before you decide to do this.

I hope the DLCs are bigger than just the one quest. Witcher 3 had tiny little DLC, but that was all free. Fallout 4 has paid DLC and should be whole areas and full factions and so on.

The Green Terror sounds hella corny. I would take something from Latin and then SciFi it up a little bit. The whole bait and switch idea is kind of silly, too. Like Green Army is tougher than the Institute but gets taken out by Raiders, which would be chill, if the Raiders were badass, but the leader hides in the Mayor's Office like a little wimp and then you single handedly destroy them, all for a weak mask? I think that instead of "Raiders" they should be a group called The Purifiers and they stomp out mutation wherever they find it. At first they show up to help you fight The Green Army, and they do. But afterwards they become hostile.

They would wear Armor made of the bones of ghouls and other mutated creatures and the tougher ones would wear Power Armor made of Super Mutant Behemoth bones and Sentry-Bot plates.
The leader would be a Power Armored Super Mutant who resents all mutants and forms of mutation because of what was done to him at the hands of The Master, over one hundred years ago. One of your possible rewards would be unique Power Armor that immediately pacifies all but Legendary mutants on sight. The Purifiers themselves would be comprised of AWOL soldiers and wastelanders from all walks of life and from all over the US, from NCR to Rivet City. All unified because of their hatred for mutants and seeing as how almost every form of life in Post-War suffers from one form of mutation or another, they have declared all out war on the entire world.

I'd rather DLC take us somewhere new and not just be an added quest in the same worldspace. That will just bring calls of 'the game was sold unfinished' and we don't need more of that. All of FO3's DLC brought us somewhere new, so I'd hope they'd continue that trend. There's a lot of potential in that area for new places to explore. The boat from Point Lookout was said to have gone up to the Commonwealth and down to the Broken Banks so a DLC down there would be nice. Just an idea that had popped up

Not bad. I think combining our ideas into one single dlc would be very good, at least in my eyes. Like the DLC starts with what you wrote. And when our character finally defeats the powered armored mutant a.k.a the leader of the Purifler. You find a note on his body and he was actually a servant of the Green Terror all along. And than this event would lead to what i wrote.

Nothing stopping you from creating a mod for this idea.

Well I mean the whole point of mine is that they track the Green Army and finally catch up with them in the Commonwealth and aide the Sole Survivor and his/her chosen faction into victory against them, only to be double crossed by The Purifiers who then use their established strategic advantages to turn-coat and attack the Commonwealth due to the high levels of mutation and stating that they plan to eradicate all mutated lifeforms, including mutated humans who show no visible signs of mutation, but still carry mutated genomes.