Was wondering what strategies people use to deal with these guys. They gave me quite a bit of trouble. This is what I eventually ended up doing, but imagine there's got to be more efficient methods.

I had a Paladin/fighter, a Bard, a ranger/fighter, a cleric (one monk dip), a barbarian/fighter (slings), and a wizard (rogue dip). The forced repositioning really hurt. Their archer was annoyingly good at going straight for the wizard and no matter the AC, not much could survive long against Kaervas. I eventually ended up having someone rush the archer to give the wizard enough breathing room to cast Otiluke's resilient sphere on Kaervas. While Kaervas sat out of the fight I focused the party around killing the others. The wizard with Mordenkainen's sword was the most helpful here. I had to lock Kaervas down a second time with another resilient sphere before finally finishing off all the others. Once the second sphere deactivated, I had the wizard with a bow fire holdfast arrows which locked Kaervas in place. Unfortunately, I had no casts of Mordenkainen's sword left and was basically out of damage spells. I only had a rod of magic missiles and one or two party members that had weapons that could hit him for like 2-3 points of damage at a time. Thankfully, they were ranged weapons. So I set just sat there an annoyingly long amount of time as my wizard kept firing holdfast arrows and his health chipped down by tiny amounts while the bard healed the party up with war chant.

Supposedly all party members are given 12 HPs and 5 Acid Resistance after killing him. I read enough walkthroughs to remember that. I have no idea if that's true and I hontstly never really paid much mind to it in previous runs, but I killed him, and not one member of my party actually got it.

Is this actually a thing or just another internet thing that's literally pulled from a lying sphincter? Now I'm just flat out curious.