Tear Jerker / Bunnicula

• Two thirds of the way into Howliday Inn, Harold learns that Chester has (supposedly) died. His reaction is heartbreaking, perhaps especially because he blames himself for not believing Chester when he said something horrible was going on. Turns into Heartwarming when he returns.
• The Reveal of Return to Howliday Inn: Hamlet was behind all the spooky goings-on. He knew his master wasn't coming back for him and that he was only being boarded until there was no more room. His arthritis prevented him from tunneling under the fence, so he tried to scare the other animals into digging a way out. Hamlet knew it was only a matter of time before he was put to sleep — he was just trying to lengthen the time.
• Also from Return to Howliday Inn, the story behind why Hamlet was left there. When the animals make a trip across town to find Hamlet's master, Archie, Archie is forced to explain that he just couldn't get up the nerve to tell Hamlet he was leaving him for good. He had to retire and go to a nursing home that didn't allow animals. Ultimately, it turns into a heartwarming moment when Sunnydale decides to make an exception for Hamlet, but initially it looks like their trek was all for nothing and Hamlet is still going to be taken back to Howliday Inn and the fate that inevitably waits for him there.
• An even earlier moment from Return to Howliday Inn. Harold is initially pretty cheerful about the prospect of going back, until he realizes that none of the friends he made during his first visit will be there, although one of them does come back later in the book.
• The subplot of Bunnicula Strikes Again involves the Monroes being involved in a community effort to save the theatre where they found Bunnicula from demolition, since it represents a piece of the town's history. They're unsuccessful, and the theatre gets torn down. It's really heartbreaking to read how, despite their best efforts, they failed to keep the theatre preserved, and the town has lost a bit of itself. It's also heartbreaking to think that the Monroes are probably just going to go about their lives, as if the theatre meant absolutely nothing to them either.
• Another melancholy undercurrent to the book is Harold's fear of change. During one of his and Toby's Friday reading nights, Toby finishes off The Final Problem, which provokes Harold to anxiety, as he doesn't want anything in his life to change. It becomes a sad, nervous undercurrent during the rest of the book, as Bunnicula becomes sick and/or depressed and Chester hardens in his resolve to take down the vampire rabbit and calls Harold a traitor when he refuses to help. One moment toward the end heightens it as the theatre collapses on Bunnicula and the attacking Chester, evoking the mutual kill between Moriarty and Holmes in Harold's mind.