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.
Complete Monster: Checker Monarch has no redeeming qualities whatsoever, and there's the fact that her entire motivation for ruining Trixie's life is pure pettiness and jealousy.
She actually gets worse after her Villainous Breakdown. First she tries to outright murder Rainbow Dash with lightning just because she didn't do as predicted in Checker's earlier plan, and then she carries out the second Moral Event Horizon listed below.
Fridge Horror: As pointed in the KPNY Radio episode about the fic, Checker uses a bees nest to attack Trixie at Cheerilee's school, meaning she knowingly allowed a class full of foals to be stung by a swarm of bees, not caring if any were allergic or not.
Checker Monarch herself is a massive source of Fridge Horror. To the uninformed, she may seem like a stereotypical Cartoonish Super Villain, committing acts of cruelty simply For the Evulz. But then you do a little research and realise that since she's based on real-life sociopaths,there are really people like her out there.
Harsher in Hindsight: In the "Through New Eyes" chapter, Rainbow Dash experienced a nightmare where she messed up a flight test, crashed, and was mercilessly bullied by her classmates Circle of Shame style. Then an episode of the show aired showing a disturbingly similar scene happening to Fluttershy in a flashback. Even the author was freaked out by the similarity!
And if you didn't hate her after that, you'll definitely hate her after she forces Trixie to make a Sadistic Choice that results in Trixie abandoning her new, happy life and being dumped in the desert — and then decides to carry out the other part of the Sadistic Choice anyway, purely out of spite.
Nightmare Fuel: The character of CheckerMonarch is downright terrifying. She's a powerful, cold, calculating and heartless sociopath who enjoys Mind Raping ponies in their dreams, and is utterly merciless in her attempts to ruin Trixie's life (made even worse by the fact that Trixie is her sister). Just about everyone Checker runs into is terrified of her, including her own henchmen. Especially horrifying is when she completely snaps at the end of chapter 9 and she plots revenge against Ponyville and Canterlot, as the red in the heart of her Cutie Mark runs off in the rain - revealing the heart to be black. What makes Checker so terrifying is that her behavior is based off of real-life sociopaths, so unlike characters like Discord and Chrysalis, there are really people like her out there.