These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Designated Hero: Henry treats his family, his teachers and most of his classmates badly.
Nightmare Fuel: In the episode, Horrid Henry and the Alien Invasion, Henry is led to believe that Margaret and several other characters have been taken over by aliens because they are acting really nice and singing a song about being lovely, going "la, la, la, la, la, la". He gets the idea the are aliens from his favourite TV show, Mutant Max, where the titular hero warns that if someone is acting lovely, they have been taken over by aliens planning to take over the world, these aliens appear to be big spotty blobs of flesh with tentacles, their human forms can be identified by their hairstyle and a twisted version of their face.. After this, there are three instances where Henry pictures them changing into aliens, with a space background appearing behind them, the first one is where he imagines Margaret changing into an alien and eating him, the second is Miss Oddbod when she says the signature tune is her favourite song, and the last Peter when he is playing the cello nad going "la, la, la, la". The last one is especially creepy, what adds to it is his Evil Laugh, and the fact that this is end of the episode, it ends on Henry's Big "NO!", making it look as if that one was actually real, though of course, it isn't.