Adaptation Displacement: "There was a book?" Yes there was, and it's actually very good. It's also rather strange that few people know it was based on a book since it mentions in the opening credits that the movie was based on Felix Salten's story...
The poster for the movie was a picture of the book
Badass Decay: The midquel did a pretty good job of doing this to the formerly solemn and dignified Great Prince.
On the other hand it boosts his Papa Wolf tendencies and has him directly take on a pack of vicious hunting dogs to save his son. Not to mention he is voiced by Patrick Stewart this time round.
Family-Unfriendly Aesop: In the original novel, Bambi learns that he must live all alone to live long and safe. He learns this one from the (supposedly) wise Great Prince, of all deer.
Faux Symbolism: The scene where Bambi goes with his father after learning about his mother's death symbolizes the end of his childhood and innocence. This was exatly what Disney was going for with that scene.
It was revealed in the Making of Bambi II that the butterflies seen in Bambi's dream sequence and at the end of the movie are meant to symbolize Bambi's love for his mother in the former and his father in the latter. D'awww.
From the book, Bambi and his father see a man who accidentally shot himself and examine his body:
"Do you see how he's lying there dead, like one of us? Listen, Bambi. He isn't all-powerful as they say. Everything that lives and grows doesn't come from him. He isn't above us. He's just the same as we are. He has the same fears, the same needs, and suffers in the same way. He can be killed like us, and then he lies helpless on the ground like all the rest of us, as you see him now."
There was a silence.
"Do you understand me, Bambi?" asked the old stag.
The death of Bambi's mom is one of the most famous tearjerkers in the history of film, to the point it's been parodied relentlessly in the seventy years since its release (q.v. the Animaniacs episode "Bumbie's Mom"). Watching the scene in context, seeing his mother give up her own life just for Bambi to survive, as well as Bambi being told by the Great Prince what happened to her is the cinematic equilivent of a punch to the gut.
The midquel also has a bit of well executed Tear Jerker, specifically in Bambi's dream sequence and the aftermath of the "Deer Call" scene, when Bambi finally comes to accept that his mother is never coming back.
Like you cannot even imagine. It can be especially easy to miss the single reference to Flower's gender early on. And then puberty kicks in, and their genders are much more obvious.
Lampshaded by Ronno in the Midquel:
Ronno: Bambi? Isn't that a girl's name?
There is the picture book of the Disney movie that actually called Flower a female, and made "her" a mother!
Vindicated by History: Thanks to extremely mixed reception from critics of the time period, not to mention the war going on at the time, Bambi, along with Fantasia and Pinocchio before it, was a huge box office flop when it first unspooled in theaters. Nowadays, it's one of Disney's most financially successful and critically well received movies.
Wangst: Bambi has this moment in Bambi II when he discovers his father was planning to send him off to live with another doe. And this is after they actually began to develop a bond with each other! And why? All because it's what a prince would do. It actually gets Bambi so upset that he basically tells his dad that he wishes he was dead.
What an Idiot!: In Bambi II when Bambi's father is telling off Bambi about having to accept living with another doe, it builds it up just as Bambi is about to leave to live with Mina as if he was going to say "Remember, you are my son." What does he tell him instead? "Remember, you are a prince." However, It's made clear throughout the film that The Great Prince is a slow learner, and he never had any experience raising children before. Also, he may have been trying to sever his own bond with Bambi at the same time while saying that line. And it doesn't stop Bambi from running back and nuzzling up near him before he leaves, though.