In my story, Scalba of the Talanari, there's this huge plan to conquer Romanal, a united continent, and wipe out the knight mages, the so-called guardians of peace. My protagonist's father, Dranolin, is in on it. His contribution was to allow mancers to use him as a model for creating idealized replicas of humans that could be grown from seeds to be soldiers. Meanwhile, Dalgorax is making alliances with the Gentathinian nations, because Romanal can't be defeated by one nation alone and all of Gentathine needs to be united against it in order for Romanal to be overthrown. The mancers of Car'rawd, a Gentathinian nation, are helping Dalgorax develop a magical superweapon. The only problem is I don't know what the superweapon should be. I know it should be big, but portable, and preferably be able to be taken out in one well-placed but seemingly impossible shot, and above all it should feel right at home in a medieval fantasy with dragons and elves.
Some inspiration from Final Fantasy 9 The only limit with fantasy is imagination, really. Could make magical versions of real superweapons (magic nukes); summoning of powerful creatures like super dragons or fire gods; open a portal to hell that monsters spill out of; freeze an entire city in ice; transport an entire lake of water above the city and drop it down; torrential lightning storm; massive hurricane, earthquake, other variant of a real natural disaster; plague of locusts.
Hm, actually, I think I really like the idea of an artificial storm creator. Maybe a floating pyramid that spits lighting and hurricanes out the bottom.
Maybe some kind of trebuchet variant where instead of simply pulling back and releasing something physical, they require people to perform an elaborate rite that requires blood and chanting. They need many high level mages all performing the rite at the same time in order to create the magical tension that pulls it back into a bloody magic circle where it will be loaded with some kind of hell beast egg with a bunch of pulsating spirits ready to be birthed once it reaches a certain velocity and then cracks, spewing demon babies all over. Gives plenty of time for suspense and also plenty of time to line up that perfect shot that takes out the head mage, borks the trajectory and ends up blowing itself up... or something. Alternatively, dogs who shoot bees out of their mouths.
I like the idea of trebuchet variant. With greek fire ammo it would be almost a weapon of mass destruction. With different variations of biological ammo it would definitely be a weapon of mass destruction. (Alive rat's with yersina pestis or...) With cursed food as ammo it... And you can build it, take it to parts, build again... You don't need to drag all the counter weight if you don't want to. You can have slaves in it's treadmill... Vote for trebuchet.
Maybe some array of magical devices that can be arranged around a besieged city to evaporate the water inside a la Batman Begins. They would need all five, six, seven (how ever many you want) to complete the process, so the protag could realise they only need to destroy one to stop it... And planning for the future, a new threat can be established by rebuilding the one that was destroyed.
I've always been a fan of Mana Cannons, personally. You could always have it on a big floating pedestal that the mages who charge it carry around if you need it to be mobile.
Well... i have three scary words for any magic involving world where magic rulers dictate and rule. Edit: ops forgot the 3 words: "magic nulification object " I'm assuming your magic has a source? How about a portable gem, imbued with the power of x mages all focusing on cutting a person/construct/ magic item from the source of magic. Turns out enemies kinda pale when you then have magic and they don't. Plussssss it gives you the opportunity to then have the mc get it at the end. And have him face a moral dilema. Do i use it to remove posible treats in the future? Or is magic useful in other ways. (Also do you want to write a second book or not. Hahahaha)
I think I have an idea. What about a stationary temple that can call down meteorites on any location? Kind of like a nuke silo, except it pulls its missiles out of the sky instead of shooting them from the base.
Demons/Daemons are magic, and tough as nails. So perhaps look into enlisting some help of the bigger ones to go waltzing in for a bit of a smashy smashy, and soul collection or something.
Daemons in my story are just another fantasy race, although most of them do have the deep magic in their blood. One of the main mentor figures/antagonists is a daemon.
