Kylo Ren has the makings of a great foil to our heroes in new Star Wars canon. He's walked the light side and the dark, he's got a rather personal stake in the affairs of the Skywalker clan, and he can stop blaster bolts with his mind. All of these traits make for a wonderful foundation, but when it comes to actual, bald-faced menace the wavy-haired and well-condition Vader-in-training leaves something to be desired compared to his predecessor.
Luckily, there's no shortage of newly created Star Wars villains to fill the gap left by the emotionally overwrought junior antagonist. Villains like Black Krrsantan, for instance. The dark-haired wookiee warrior won't likely win any philosophical debates. But Black Krrsantan fills an important gap in Star Wars public opinion.
Wookiees, you see, seem to have a reputation for death, dismemberment, and bad tempers. Yet usually we only see friendly, furry hero Chewbacca fighting on the side of the angels. And while he may lose his cool from time to time, Chewie never pulled the arms from anyone's sockets that didn't deserve it.
Not so with Black Krrsantan. Like a lot of unfortunate wookiees the black-haired bounty hunter spent more than his fair share of time as "entertainment" in fighting pits. Unlike most of his kind, however, Krrsantan enjoyed it. So much so that he still murders the occasional contestant, takes their place, and murders their would-be opponent for nostalgia's sake. Not to mention a sick wookiee's sense of symmetry.
Black Krrsantan was last seen in the employ of a pre-asphyxiation Jabba the Hutt. There he was considered a bounty hunter at least on par with Boba Fett, and wound up nearly crushing Chewbacca's skull with a very large rock sample.
Meaning when it comes to old fashioned criminal violence he does both the metaphorical and literal heavy lifting.
On the topic of goatee-sporting antitheses to Star Wars heroes, here we have 0-0-0 and BT-1. While that's technically two characters this droid duo comes as a package deal in much the same way as their obvious, clear-conscience'd counterparts C-3P0 and R2-D2.
0-0-0 -- Triple Zero to the people he doesn't kill -- is the taller of the two. He has the personality of a centuries old protocol droid with one minor design flaw: poking holes in organic life forms to collect their vital fluids. He's also very bad at holochess, and aims to make up for it by being a legendarily sore loser (by assassinating anyone that beats him).
BT-1 (Bee Tee), on the other hand, pretty much works exactly as intended. The tin can on roller blades is an assassin droid thinly disguised as an astromech. Which, along with his impressive array of weapons tucked away inside his trash bin frame, earned him the loving designation "Blastromech"... before he vaporized everyone who gave him that particular handle.
The idea of an evil R2-D2 and C-3P0 under the employ of Darth Vader should be too silly, even for Star Wars. Yet somehow... It works. Triple Zero's sadistic streak, as well as Bee Tee's energetic love for carnage, just come across entirely too sincere to feel like a gimmick. And while they have much in common with another fan favorite murder-bot something about the very descriptive way they dispatch their targets has more bite to it than the canonically questionable HK-47.
And, yes. It certainly doesn't hurt that they're in the entourage of Darth Vader, the cyborg that wrote at least one edition of the book on "menace."