Mixels are mischievous creatures who live in tribes of three. They have the ability to combine with other Mixels, either within a single tribe or cross-combining to gain another tribe's abilities. All that is needed to combine are willing Mixels and a magical square known as a cubit. The colorful creatures have to look out for Nixels, who consider themselves superior and like to destroy Mixel combinations. Major Nixel, the group's leader, throws and kicks his underlings to steal cubits.
Nothing gory but a Mixel's eyes explode into fire and in Calling All Mixels there's an animation where one gets so angry that their eyes inflate and pop.
One of the creators confirmed that Mixels are non-binary so any time where they're referred to with pronouns other than they/them could be misgendering. There's one part where a Mixel says "Hello ladies" directly to the viewers which could be triggering if you don’t identify as one.
Cis actors play non-binary characters. Chomly’s design might be a racist caricature (he’s a brown Mixel with a gold tooth who lives on a farm). The aforementioned farm also uses totem poles which is cultural appropriation.
King Nixel is the only character who (probably) gets killed and technically he's a "black" guy but it's revealed earlier on that Nixels are white monsters in black shells.
Meta example; Shuff and Krader crying are played for laughs, Flain immediately presents the latter with a solution to his problem which is a great thing but he doesn't show too much regard for his friend's sadness, either.
Fantastical hate speech towards the Mixels by the Nixels as well as attempted genocide. The Nixels are somewhat fascist-coded and the Mixels are heavily associated with rainbows so it could be triggering.