dolphins are the only Always Chaotic Evil beings that we know of.
OK I'm just gonna say it.
I genuinely
hate (OK 'strongly dislike') when people try to apply human morals to WILD ANIMALS as if they operate under these same morals or even have the ability to understand the concepts of 'good' and 'evil', even if they are doing it as a joke.
Are there reports of dolphins doing things we would consider 'evil', like ganging up on female dolphins and raping them? Or groups of dolphins killing harbour porpoises for seemingly no reason other than to kill them? Yes, there is no dispute about this.
But dolphins are also very well-known for protecting and saving humans, in Greek mythology they were viewed as being helpers of humanity. And it's pretty easy to find stories of dolphins helping injured divers or swimmers get back to shore or even protect them from a potential shark attack.
Hell back in 2018, a group of dolphins protected a mother humpback male and her calf from a group of male humpbacks that wanted to mate with her.
And really most of the 'evil' things people love to bring up that dolphins do
aren't even anything unique to dolphins. Tons of animal species are known to engage in coercive mating (what we would call rape), cannibalization, or even infanticide. But would you blanketly label these animals as all being 'evil'? No, because they don't have the same morals as humans do and, for many animals, it's doubtful that they have a concept of 'morals' at all.
Personally I think this whole thing just comes from how we view dolphins (and other animals we deem as being 'evil'). Humans generally view dolphins as being 'cute' and when we learn that these (again, for emphasis) WILD animals sometimes engage in behavior that we would consider to be abhorrent, we immediately make the assumption that their 'cuteness' was just a front for their 'secretly sinister and evil nature'. But this is ignoring the fact that
dolphins didn't evolve to be cute, that's just what they ended up looking like over tens of millions of years of evolution. It's a complete coincidence that the modern appearance of dolphins matches the general human concept of 'cuteness' and eating up all the rhetoric about the 'cute' dolphins can make it easy for people to forget that they have just as much capacity for being dangerous as 'ugly' animals and both deserve the same respect during potential interactions.
Also there are like 40 species of dolphin and not all of them are known to engage in these 'evil' behaviors like coercive mating or porpoise killing (the latter of which isn't even common and IIRC was just the local population of bottlenose dolphins near Aberdeen, Scotland that were doing it. There's no evidence that bottlenose dolphins, or even dolphins as a whole, regularly engage in the killing of porpoises)