MIne would be one of those gag bossfights where she falls down a flight of stairs and dies after an epic transformation scene.

Given how my kobo in Pathfinder has been doing lately:

Failed will save that results in him or his eidolon being removed from the fight (Fear, Command, Suggestion, etc)

Well that would depend on which character.

1. If it's on Tragen the main character of my life's work. It be like fighting Rambo as like Rambo he's a master of Guerrilla warfare and fighting him in close quarters is suicide because his fighting style can be best dest describe as the swordsman style resembling Gerald of Rivia, tomahawk and knife fighting resembling Connor Kenway, and martial arts resembling Jake Muller. In short you are the prey and he is the hunter and you must survive against his deadly unpredictable tactics and lethal fighting skills however way you can. You must try to outwit him before he outwits you.

His boss music would be this: https://www.youtube.com/watch?v=rTiK8ajVVVc

2. Against Vardock one of the main villains and later main characters of the series and Tragen's adopted brother. As the most powerful magic user in the world he lives in, possessing destructive powers that are on par with that of a god but still possessing a mortal body. You would have to accede his powerful and destructive spells and waite for him to tire out, only then can you rush up and deal damage but he can instant kill you with any spell he casts and will always have protective barrier up and flying untill he grows tired and is vulnerable.

His boss song would be this: https://www.youtube.com/watch?v=RSt2ZQSpDz8

3. Finally against Damen would very much be like the Alien from Alien Isolation. As a terrifyingly skilled assassin and a absolute master of stealth to the point of haveing almost supernatural skill with it. It would be more of trying to survive within a certain amount of time. You would have tp desperately avoid the darkness anyway you can however wya you can because once you step into the shadows your dead, and must not stand out in the light for him to pick you off from a distance. Your best bet, would be to hide from him and somehow create distractions. But be warned he adapts to whatever you use so he will never fall for the same trick twice.

His boss music would be these three depending on if he's stalking, alerted, or has spotted you:

(Stalking): https://www.youtube.com/watch?v=lxb1ofLKqG0

(Alerted): https://www.youtube.com/watch?v=VbTzV2XIcYE

(Spotted): https://www.youtube.com/watch?v=ZXYhcg5Jyv0

Draekon would pretty much be a raid boss encounter.
You'd need to defeat her before the fight progressed for too long, else she'd build up to a singularly powerful attack that'd wipe you out in a single go.
Pair that with her wide range of abilities and skills, and you're in for a tough time.

You would encounter the stealth suit clad fennec in the forest, face half hidden by one of them quad nvg sets. Even tho it's daylight out. He would attack with suppressed weapons from whatever direction you're not looking. Your only hope is to deploy your tactical cardboard cut-out pinups to distract him and get your damage in! Then, when his health is low enough he'll leap from the bushes in a final knife attack! You must disarm him with the special phrase your learned off the General's computer (Who's a good lil fenfen?) And then he'll die of embaresment!