Complete Monster: Bonifer Squoon, so very much. He used to be a shy, bookish man who was friends with a man named Ortham Wingfeather. He was in love with a woman named Madia, and was enraged when she married Ortham. So he pretended to be Ortham's faithful advisor, all while secretly plotting to make him suffer. Madia had two sons, one of which, named Davion, was born severly deformed. Despite this, Madia loved both of them. However, Squoon kidnapped Davion and told Madia he was dead, then, along with the evil Ouster Will, with whom Squoon was conspiring, he raised Davion through lies, claiming that Madia never loved him, because of his deformities. Davion believed these cruel lies and grew up to become Gnag the Nameless. And that's just the beginning. He's also the one who helped Gnag's army get into Anniera, causing the invasion that supposedly killed Esben. In The Monster in the Hollows, he kidnaps a little girl. In The Warden and the Wolf King, he turns himself into a Giant Spider and tries to kill Janner and Kalmar! He is the "monster" referenced in the title of The Monster in the Hollows, and holycow, does that describe him perfectly!
Tear Jerker: Nearly every death scene. Despite there being a lot of deaths in the series, it never gets old:
Nugget's death is sad mainly because it's always sad when animals die.
Esben. Everyone thought he was dead, and when he is finally revealed to have been alive the whole time, he doesn't last long.
Podo Helmer. The worst part about his death is that it shows us just how callous Yurgen really is.
Surprisingly, Gnag has a sad death, mainly because of how much the guy suffered.
Janner. This one was very unexpected. This troper had to read that part a few times just to make sure he had read it correctly. It's also kind of a Crowning Moment of Heartwarming, because after reflecting on how selfish he's been throughout his adventures, he finally sacrifices himself to save his brother and many others. Fortunately, the epilogue makes it better by implying that Kalmar has found a way to bring him back to life.
Woobie, Destroyer of Worlds: Sure, Gnag does some very evil things, but can you blame him after all the crap he went through in his childhood?