A small mod addition that I've had on my computer for a while, but haven't bothered releasing. It's the Endbringers from Worm, coming to destroy your fortress!
Three overpowered megabeasts that will show up very late (their requirements for attack are twice as high as other megabeasts). They aren't completely unbeatable, but are
extremely powerful and if you're not prepared they will almost certainly spell doom for your fortress in a spectacular way.
I'm spoilering the details and strategies because they have some pretty crazy powers and you might want to be surprised.
There are three creatures in this pack. All are simply called "Endbringer" because they will get their own names in-game.
All three are constructed of multiple protective layers surrounding a vulnerable "core". The outer layer is as hard as aluminum, the core is as hard as legendary metals. (No, they are not as durable as they were in the original story, I wanted to make them possible to hurt). They also possess a potent healing factor, capable of fully regenerating in a matter of minutes, and are all able to avoid traps and webs.
You're going to need lots of adamantine-using legendary warriors and/or some clever dwarfy mechanisms if you want a chance at winning.
Behemoth: The slowest of the Endbringers, a moving mountain with power over all forms of energy. It radiates an unblockable "kill aura" that will flash-boil any creature that gets within a few tiles, making melee attacks impossible, and its lightning attacks will make short work of those trying to attack at range. Also, it can spawn magma periodically, and periodically emits radiation that will slowly kill anyone who manages to survive the fight. While an endless assault of adamantine arrows may kill it eventually, luring it into a trap like a cave-in is probably your best course of action.
Leviathan: A fast-moving amphibious Endbringer that spawns water on its own tile with every step while in combat, quickly flooding the arena. It can also use hydrokinesis to push any creature that is standing in water. Combined, this creates a deadly combo that makes melee assaults all but useless. It's smaller than Behemoth though, so a non-stop onslaught of adamantine bolts can kill it eventually. You can also try dumping magma on it while it's in combat, tricking it into obsidianizing itself, although it's smart enough to refrain from spawning water while it's actually submerged in magma.
Simurgh: A flying Endbringer in the form of a woman with many wings. Smaller than the other Endbringers, a group of legendary warriors with adamantine weapons and armor may be able to win...but this victory comes with a price. Simurgh's power is a song that will cause personality shifts and unpredictable behaviors in anyone who took part in the fight - some effects which may be contagious, and some which may not show up for years. Even if you win, it can still destroy your fort later...
