What lies below is spoiled just in case my players happen to be reading this. That's because, despite the subforum I'm posting in, this has some very mild Age of Worms spoilers. It won't spoil anyone else, but I'm doing some foreshadowing in my game and my players would learn more from this than they should.
I'm just curious—could this red dragon be slipped into Shackled City? His motivations are just kinda general "evil dragon" stuff. It could work as a sideventure, I suppose. It'd be cool to tie the guy in to two separate APs.
Zenith Trajectory has Gottrod, a young adult red dragon.
Zenith Trajectory has Dhorlot, a young adult black dragon.
Foundation of Flame has Hookface, a mature adult red dragon.
Thirteen Cages has Moltenwing, a mature adult pyroclastic (redish) dragon.
Gottrod and Dhorlot definitely do not fight to the death.
Hookface can but it doesn't really make that much sense for him.
Moltenwing is just being a mercenary and isn't being paid enough to die.
Of course, you could switch Brazzemal in for any of them if you want and change his motivation.