Game Of Thrones Season 6: Ranking Every Death From Worst To Best
11. Three-Eyed Raven (And The Children Of The Forest)
Cause Of Death: Stabbed by the Night King's magical ice blade; mauled by wights/died in explosion allowing Bran to escape.
I suppose you could argue that the Three-Eyed Raven isn't dead, since Bran is becoming him. But this version of the Three-Eyed Raven, the one with Max von Sydow's wise ol' face, is very much gone.
Although he was only there to guide Bran through his visions - and interrupt them just as they got going - von Sydow at least brought some weight to the role, and his death meant getting to see the Night King make a kill up close and personal.
Similarly, the Children of the Forest - and in particular Leaf - were an important part of the mythos of the White Walkers, shown to actually be their creators (a plot point that was overlooked in the aftermath of some of the other developments from The Door, but is a major reveal nonetheless). They went out fighting their creations and saving Bran, and now are, quite probably, extinct.