Series Part 6 - Looks like we discovered the crux of Hot Coldman's final plan: Mammal Core developed by Dr. Strangelove looking for a "final will" of The Boss through its development into Peace Walker's brain, but after all this, she does escape because Big Boss let's his emotions get in the way
And as a reward, he has to fight Chrysalis, the helicopter death machine that has been terrorizing the plot ever since he saved the Sandanistas from that boathouse and in that case, I was all ready to finally put this thing in its place.
But on top of being plot-important, Chrysalis is also one of the deadliest aerial bosses I've ever seen since half of its attacks are completely broken, add in that instant dodge move it has and this fight's all about just breaking the player over a fence and having a blast at the expense of the player.