"Cuộc phiêu lưu" sounds really weird, as though he was saying "cuồng phưu lưu".
Turtles needs an apostrophe here, since it's possessive. "The turtles' adventure"
There is nothing wrong with the pronunciation of "cuộc". It is correct...if you are in North Vietnam. You will not hear it like that in South Vietnam. Even common words like water, "nước" are pronounced differently in Vietnam. No big deal. Every language has regional variations. Eg, in US "balled" peanuts in the South are pronounced "boiled" peanuts in the North.
I'm not a native but cuộc sounds different here than in previous audio examples. It sounds more like cuộng like one poster mentioned and my northern friends confirm that is incorrect.