3x03: Goblin's Gold. I know there's been plenty of 'what's up with Season 3 Morgana' on this page, but this episode stands out in particular. A verbatim transcription follows:
Goblin!Gaius: Merlin has magic! He's a sorcerer! You should arrest/execute him!
Morgana: *behind an evil smirk, of course* Hmm, this makes so much sense. Merlin, a sorcerer? Now I know how he was able to escape my sister and why those random rocks fell on me in the catacombs. In fact, now that I think about it, lots of weird stuff happens around Merlin. And he was very helpful when I found out I had magic and wanted to protect that Druid boy too! All that talk about "using magic for good" and "understanding how I feel" in the catacombs makes a lot more sense now!
Normal!Gaius: Never mind. I was possessed by a goblin and didn't mean a word I said. Merlin is not a sorcerer, you should just forget I ever said that.
Morgana: Okay. Sure!
- Really Morgana? Really?
- This is the reason why Morgana in season 3 was so frustrating as a character. Perhaps we would have been more accepting of Morgana as an unrepentant villain if she were actually, you know, good at being an unrepentant villain. Instead she's a one-dimensional Smug Snake with an annoying smirk, little to no intelligence, and a success rate of zero.
- The problem with that idea is that letting her win at all just isn't an option. There's no buildup in her villainy. It's always almost straight to "kill a main character", and that outright can't be allowed. If she had done some more subtle evil acts, like maybe killing a few scouting parties or something, it would be easier to appreciate her as a villain.