Often, the third season of Watership Down has been critizied, because it's far away from the first two seasons and had nothing to do with the books. Not only the animation style has changed, the series gets darker and broughts in supernatural powers.
Some like the new direction of the series, others are annoyed and often, the unlogical progress has been critizied. But when we take a closer look to the story and the events, we will see, that the third season is told logical and comprehensible very well. You have to give your own thoughts to it. Because of that, I want to analyze the third season a little bit.
Campion gets smashed by an rock im episode 2.13, after he saved Woundworts life. In the next episode, we can see, that he is alive and completely scarred. It was criticized, that his scars are completely over the top, because he ony got buried.
But Campion was not only buried, he died in the caverns. Why should he face the Black Rabbit of Inlé else? It assigns Campion with the task to handle Woundwort over to the Black Rabbit. And why didn't the Black Rabbit do the job by itself? Because it could not access the world of the living. And so, it chooses someone, who should be dead: Campion.
The flashiest things in season 3 are Campions scars. Many think, that he got them by the rock, that smashed him. But this makes no sense: No one gets so scarred by a rock. Campion got the scars from the Black Rabbit of Inlé.
And for a good reason: Spartina met Campion and thinks, he is the Dark One. So she brings him to Darkhaven, where Campion met Woundwort. If Campion was not scarred, he won't be able to get to Darkhaven because Darkhavens owsla would have killed him otherwise.
Annotation: Woundwort has both eyes, when he left Darkhaven. Anyway, the Darkhaven rabbits know, that Woundwort is an one-eyed rabbit. It's not clear, how they could know this, but I think, reports of an one-eyed rabbit with affinities to Hemlock, Woundworts father, have reached Darkhaven.
In the third season, Silverweed has a bigger role. He has powers, akin to Fivers. The difference is, that he could not see the future, but the trail of fate of an animal, if he touches it. And he is able to read minds. Because he has akin powers to Fiver, he could not only read his mind, he's also able to control Fiver. This works in the reverse way, too.
This idea has it's source in episode 1.03. Fiver says, that something is strange about Silverweed ("Silverweed! He smells like autumn, like dead leaves"). In the third season, this was expanded to the visionary abilities of Silverweed and the soul-connection between him and Fiver. This idea is adventurous, but it fits in the third season.
The idea with the magic is not originated in the third season. Already in season two, it was alluded, that something like magic exists. (Trembling told it Pipkin, when he tries to fly - episode 2.10)
So why use a turtle and call it "Hedge the Wizard"? Take a look at episode 2.07. I think, they took a turtle, because it can get very old and could be very wise. The name "Hedge the Wizard" arises in the Hedgewizard (Hannah dressed up like an Hedgewizard to trick Vervain).
Hannah learns from Hedge the spell, that opens the gate between the world of the living and the shadowland. Although the spell says it, Hannah didn't know, that she will die, when she speaks the words. When she met Woundwort and his army, she could speak the spell. Instead of her, Silverweed will unchain the magic in Watership Down. But why didn't Hannah end the war earlier?
This question is irrelevant. The Black Rabbit of Inlé knows, who will die, when he will die and where he will die. It knows, that Silverweed will unleash the power in Watership Down. Because of that, it is so important, that Campion leads Woundwort and his army to Watership Down.
That Silverweed will die in the end of the series, should be beyond all questions (even, if we didn't see it). The Black Rabbit has told Campion, that someone must call it, so it may claim, what belongs to it (Woundwort) and that he who calls it must surrender to the Black Rabbit of Inlé. And Fiver has a vision about it: "Neither claw nor fang will win the day, only words can save the world today. But the price of words will cost tomorrow, a friend will pay and we will sorrow!"
For further cementing of this statement, you find subsequently a dialogue between Campion and the Black Rabbit of Iné:
BR: "You will live and your friends will live. But one among you must call me from the Shadowland, so I may claim, what is mine. And that one must surrender to my dark embrace."
Campion: "I give you all my tomorrows, Black Rabbit. Take them, if it will save Watership Down!"
BR: "They are not yours to give, Campion."
When you take a look on the third season, you see, that it is not so irreproducible like before.
And I know, that the progress of the series wasn't planned in the beginning. But you must say, that the third season ends closing. Every question is answered and no cliffhanger bothers the overall picture.