Stephen Chow's Mermaid is a fantasy-comedy-romance with an environmentalist slant, and in the year of its release (2016) became the most successful movie in China's box-office ever. Newcomer Lin Xun plays the title character Shan, the mermaid.
In this movie, business tycoon Liu Xuan is trying to turn the Green Gulf into a fancy-pants property development, which is a bit of a problem because the Green Gulf is a wildlife reserve and the home of a community of merpeople. These merpeople aren't taking this lying down, and they send one of their own, Shan, out into the human world to lure Xuan and assassinate him. Basically, I think of this film as FernGully, only where Crysta is on a mission to assassinate Zak. Of course, the mission doesn't quite go as planned, for Shan learns that Xuan has more nuance than she initially thought, and Xuan is drawn to Shan's adorable, earnest ways.
Stephen Chow is known for his over-the-top slapstick humour and heart, and there's plenty of that in this film, with Shan getting up to some hilarious antics in her attempt to kill Liu Xuan before that turns into a romantic comedy. But the film is also unapologetically aggressive on the importance of environmental protection, with some pretty violent and (I believe) intentionally disturbing sequences at the end when the merfolk are attacked for simply being in the way of progress. It's a heavy-handed kind of film.
The merfolk in this film live in a shipwreck tucked into the Green Gulf, as Xuan's development project has made it impossible for them to leave. They're suffering and dying slowly, and Shan is their last hope at finding a solution, which makes the stakes of her mission pretty high. Unlike most mermaid-focused media, Shan cannot and does not turn human at any point. Instead, she's learned to "walk" on her tail, which means she stuffs her two fins into two wellington boots and shuffles along slowly, or she uses her skateboard to help out. There are a few underwater scenes but those scenes are meant to be functional, not awe-inspiring underwater eye candy. Those scenes are also heavy on the CGI, so there's not much realistic detail of their tails. The really HUGE tail as seen in the poster and the trailers isn't Shan's, but the clan's powerful grandmother matriarch. A cool thing about the CGI, though, is that Shan gets to swim really fast.