Reading these expositions about people’s evil dark urge, I will present you with the only character I have done an evil durge playthrough with.

I give you Gnomelander:

[Linked Image from i.ibb.co]

Spoilers and content warning for references to murder and incest below.

Gnomelander is a gnome (obviously) sorcerer who was raised in the Bhaalist cult and ever since he was a child he was subjected to experiments and torture to produce the most brutal and sociopathic murderer possible. They went a bit overboard and he became a bit too unhinged, even for a Bhaalist cult, to the point where they had to capture him, lock him up and use magic and drugs to subdue his mind and turn him into a harmless vegetable. As a result of the abduction to the Nauthiloid and the insertion of the mindflayer parasite he begins to slowly regain his mind and memories and now there is a weapon of mass murder on the loose, and he has a bone to pick with some people.
Gnomelander’s personality is murder and narcissism. His go-to response to most situations is Eldritch Blast. If he is annoyed - Eldritch Blast, if he is bored - Eldritch Blast, if he is excited - Eldritch Blast.

Here are Gnomelander’s unhinged and unfiltered views of the companions.
DISCLAIMER, Gnomelander is a horrible and despicable person and his opinions should generally not be adhered to, by anyone. They do not reflect the opinions of his player and should not be inferred as factual or serious opinions about the companions.

Lae’zel - Are all Githyanki this daft or did I just happen to run into one that was hatched from an egg that was dropped a few too many times? At least she had the decency and good taste to have sex with me. But, what just happened? Vlaakith is a fraud that has been lying to her her entire life. Oh, that’s just priceless! You must be furious, why don’t you work some of that anger off by maiming some people for me.

Shadowheart - By the shiny balls of Carl Glittergold, just shut up about Shar already! I know this type, little princess with abandonment issues looking for attention. All she wants deep down is for mommy and daddy to praise the horribly ugly artwork she made in nursery school. Just toss her a bone every now and then, pretending that you actually give a shit and she will follow you around like a lost puppy. I can see why she and Scratch get along so well.

Astarion - Oh, thank you Cazador for doing the legwork and breaking this one for me. A perfectly miserable and empty husk of a soul delivered right at my feet just when I needed it. All too eager to indulge in every little temptation to bloodlust and cruelty that I dangle in front of him. Making him do whatever I want is as easy as making a drunk halfling dance, which I have done many times, because I know charm spells. And the fool thinks I am actually going to help him ascend.

Wyll - Who? Oh that vigilante who decided to jump off the wall that provided him with a tactical advantage and join the fight against the goblins on the ground instead? Only to instantly get shot in the face with an arrow (worth noting that Wyll can actually permanently die in that fight if a goblin gets a lucky crit on him, and no re-loading in honor mode so). You are saying that was the son of Ravengard, I hope Volo was taking notes on that absolutely pathetic way to go.

Karlach - What now? You are saying she wasn’t actually a devil and those charming people were not actual paladins of Tyr. Oh well, I still got a nice sword out of it.

Minthara - Finally someone with a little ambition and vision! You also sound like my mother, which, frankly, is making me kind of turned on. This Absolute cult sounds like a nice gig, but your bosses are kind of a bunch of rotten dicks. What do you say we take control of this elderbrain thing and run the show instead?

Halsin - Can everyone please stop pestering me about saving this damsel in distress? Sorry, but Minthara gave me an offer that just sounded so much more amusing. The smelly old bear can stay in his cage and rot. Besides, bear fur gives me rashes.

Jaheira - Wait, this lady who looks like a retired art teacher is Jaheira? The Jaheira who defeated Sarevok and Jon Irenicus? Sheesh, go knit me a sweater grandma!

Minsc - Oh, he comes already delivered with tadpole insertion. How convenient, let's just leave that in there. And Boo was absolutely delicious, though there wasn't that much meat on him.