The changes between Matau in LoMn and WoS are interesting, and I’ve found myself analyzing him the last times I watched either.
In Web of Shadows, Matau suddenly becomes much darker, losing his Airy quirkiness and gaining personality traits more comparable to those of Ta and Po characters. The change itself doesn’t strike me very hard, but when I think about their explanations, Matau’s story suddenly becomes a little sad.
In WoS, Matau is always complaining and grumbling about Vakama, and develops a pronounced pessimistic view towards everything. He’s questioning Vakama’s leadership, which I took to be partially due to lack of attention. He wants to be noticed and acknowledged by the others too.
Worse, however, is how he reacts to Nokama. When she comments that they made it to Metru Nui, he replies sarcastically with “whatever”. When they’re in the cocoons, he rolls his eyes when she says it’s not Vakama’s fault. When Nokama says they’ll be fine as Hordika, he outright flips out. All of us know that Matau had feelings for Nokama (screw canon!) in LoMn, and in WoS, she’s always defending and worrying about Vakama. Matau is deeply jealous because of that, and as a result, he becomes aggressive and sarcastic as a defense mechanism, burying the feelings he has for her in an attempt to convince himself that they aren’t there.
Every once in a while, Matau attempts some humor (e.g. “Guys, look it’s amazing! It’s Keetonguuuuuu! …. Not.”). These attempts are always met by aggression, sarcasm or a life lesson from Norik. He’s still trying to be himself, but everybody is making it difficult for him, and as a result his defense mechanism kicks in again. When Nuju comments on the sounds of the night, Matau responds with more sarcasm. When he’s told to be patient, he blows up and runs ahead of everyone. Even when Keetongu found something he said funny, Matau covers it up!
I never appreciated how much duress Matau was under in this movie when I was a kid. Now that I’m looking at it like this, though, I can appreciate just how hard it all was for the Toa of Air. This movie wasn’t just dark atmospherically and thematically. Vakama wasn’t the only one battling the beast within. There was a dark beast in all the characters, but in Matau, it manifested itself as a psychological issue so ordinary to us that it escaped all of our notice.