This isn't just some murder run where everyone dies. Reddit user Sparkism (who rather fittingly has the 'Bhaal' flair) specifically devised a step-by-step plan to make everyone in the Sword Coast as miserable as possible. It's meticulously detailed, breaking down the choices required act by morbid act.
The run begins with a few obvious steps—don't get Shadowheart out of the pod, don't rescue Gale—but it quickly takes a dark turn with commands like "pick up Astarion, he'll be important later," and "recruit Wyll. He's an important piece." This is immediately followed up by the step: "Let Arabella get bit. Steal her body and show it to her parents." Shot and chaser.
Sparkism doesn't pick sides, either—after all, routine evil is so pedestrian. Remember the tiefling by the telescope, the one who nearly gets ganked by a bugbear assassin? Sparkism recommends you kill the bugbear, steal her soul coin, and then hurl her off a cliff. Indeed, they aren't content to just lay waste to the Druid Grove like any power-hungry source of evil.
"Set the Gobs on the grove. Turn on Minthara. Wait until the tieflings are massacred, then save whoever remains. Send them off and party," Sparkism elaborates that this is for the "delicious Kagha cutscene", which I assume is the one where Arabella's parents exact their vengeance on her, and not some dark outcome I'm unaware of because I'm not fantasy Joker.
Perhaps the pettiest suggestion they make is this: "With Laezel in the party, go to the mountain pass and speak on her behalf whenever possible." Incredible.
I won't spoil the rest of the thread, because it just keeps going, but it's an incredible read. It's like watching a car crash in slow motion—except someone orchestrated the car crash, wrote a car crash manifesto, and showed it to you after they were acquitted of all their crimes.
The one glimmer of hope in Sparkism's dark design is that they spare Scratch from an ignoble fate. They pick up the puppy early on, who presumably sticks around because he's incapable of comprehending the true evil set before him. The last step in Sparkism's 75-point plan for misery is to "Dominate the world. In Scratch’s name."