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: Mr. Pupa, in almost all of his appearances. It's one of the few things almost all of the works and canons agree on.
While Mobster Kingpin doesn't appear nearly as often, Wigmund canon has him as one when he does. One fic has him listed as one of the only pure evil figures of the city (Mr. Pupa, predictably, is another), he owns a portal to Hell, and it's implied that he has children raped on stage in front of an audience for their amusement.
MK gets even worse in Heart Full of Empty, where he plans to nuke the city so that demons can take over Earth.
"Funny Aneurysm" Moment: Seeing as Gamzee is a fountain of these already, it's only fitting that there'd be one here. Sober depicts him snapping out of his sopor slime state and becoming a smart, calculating Awesomeness by Analysis fighter, singlehandedly beating off some Felt members. This is presented as a Crowning Moment of Awesome. However, this wasn't too long before the canon revealed what sober Gamzee is actually like.