Regis and Milvia from the Baptism of fire
Both these characters came across very strong. I loved Milvia's attitude, her bowman ship, and she was a very thoughtful independent woman I also like the fact she wasn't into Geralt. Hopefully CD keeps it that way or you have to impress her beyond go hunt down 5 animals and get several furs that would cheapen her character.
Regis loved him! Seriously him and Geralt make a dream team! Maybe its the whole Vampire + Witcher teamup here but they start out ice cold but become very good friends and even have moments where Geralt turns to him for advice, support, or help I really like the fact the witcher finds comfort and wisdom when he chooses to ask the vampire knowing he's got way more experience life wise then the whole team combined hopefully they keep his attitude and Geralt's repour in tact.
These two should be recruitable as game long team mates.
I'd also love to be able to invite either or both of these team members to go hunting with me when I'm on contract jobs it will make the fight harder the more I bring friend wise but I will be able to spend time with them, get banter, improve our group fighting, and get more things as well as they're very helpful in a fight not just sit back and yell orders like that sorceress did with the squid. Also the boss fights need to be challenging the squid sat still let me hide for 3 days straight and didn't do anything.
Regis should be more powerful at night missions but will still hold his own just fine for day missions also the moon should effect him during the full moon as shown in the books he can do even more amazing things so if I go hunt down a a warewolf at full moon he maybe really strong but I've got Regis who is also very strong who can be a buffer so I can wear the guy down.
Some monsters should be drawn to Garelt but Regis can repel them also keeping Regis's vampirisum a secret should be something as well. They should also keep the fact that Regis can't be seen by any other use by visually like they tried to use crystal balls and looking through the eyes of a crow in the book to track the group yet they could only ever seen the humans and witcher so they kept thinking we only have to deal with four people when infact there were 5.
Regis should also be able to use his blood sensing ability all the time even around mages like Triss or Yen or Owl girl it doesn't just go away because they're powerful people. Maybe he can also let Geralt know if they're lying due to blood pressure and heart beat and if they took drugs to slow that down to fool him he should be able to smell that due to it being in the blood.
Though one thing I can say they should leave out is the whole turning into a giant bat infact no bat changing just make him be able to fly or biotic charge or something I always hated the whole turning into bats thing. But he can still keep putting people to sleep at will, confusing them at will, Jedi mind tricking them at full moons, sensing the blood, immunity to fire, fearlessness,finding hidden creature, taking down enemies with you, and of course healing you he can do this inbattle even if you can't.
Since Regis is also a doctor he has potions they won't cure you 100% but maybe 50% and they don't require meditation like your witcher potions do so you've got a back up when in a tough fight.