[DMing] I just realized my evil plan for my BBEG

Okay, so I'm running a campaign with 4 of my friends as players, together making up

• Half-Elf Beastmaster/Swashbuckler
• Human Champion
• High Elf Conjurer
• Dragonborn Eldritch Knight/Oath of Devotion Paladin There is a beloved NPC, Rorke Illan, an overly excited librarian who's been a comic relief in the story and a friend since session one. The BBEG is quite mysterious, all they know about him after an encounter with him and some info from a sentient dagger is that he's a drow man who wears a purple cloak. Now, my plan, if you haven't figured it out, is to eventually have Rorke be revealed to be the BBEG in disguise, after travelling with the party to stop the BBEG from obtaining an artifact that would allow him to summon the Fiend and let the planes bleed over, releasing all matters of things. Once he has revealed himself, Rorke will execute the Ranger's beast as a show of good fun, and then use his personal knowledge of the party to dissect their lives and cause them as much pain as possible. What do you think? Too evil? Not evil enough? Any suggestions to make it better?

Edit: Rorke won't outright kill anyone, instead, he'll be eliminating the power of some of their most valued magic items and just generally screwing with them, a way in and out of character for me making up for my over generousness with them. From our Champion, he'll be taking his Demon Armor, with which an AC of 21 has made him feel rather good, from our Conjurer, he's nullifying the magic of the Robe of Eyes that she's purchased, the Eldritch Knight/Paladin will be losing his trusty sword, Darksbane (it's uncommon and I made it myself it's not as bad as it sounds) and the Ranger will be losing his claws (not a magic item, just a very good pair of claws he crafted originally from a Nat 20 on skinning a bear and upgraded with dragon parts)