[RPG] What are the changes to a character caused by Wereraven Lycanthropy from the Curse of Strahd adventure

I'm going to attempt putting together some RAW information that I am able to find.

After reading through the relevant sections (Town of Vallaki) there is no mention of the reason for the characters appearance. Only his duties around the town (such as bullying people, and being a henchman). There is also some mention of his creepy doll collection in a few spots.

As far as the origin of his deformity - here is some information on how it started.

"One morning their father and their uncle took them fishing on Lake Zarovich. On the way back to town, a dire wolf attacked Izek and bit off his right arm." - Page 231.

It continues to mention as well that...

"Unlike his sister, Izek was born without a soul." - Page 231.

Lastly, here is how his arm was returned to him (in regards to what is written).

Fiendish Gift. After years of doing Baron Vallakovich's dirty work, Izek awakened from a drunken stupor one morning to find that he had grown a new arm to replace the one he had lost. The new appendage has barbed spines, elongated fingers, and long nails. He can create fire with the snap of his fiendish fingers and has used the flames to put the fear of the devil in every Vallakian. - Page 232

There is no actual mention as to how this happened. However, the name of the attribute leads me to believe that...

It is likely a gift from Strahd/evil beings who support Strahd.

However this is only a guess currently. It has been pointed out in the comments that additional fluff information exists in AD&D2E regarding evil acts committed changing your character in fiendish ways. This looks to be what is happening, and almost certainly is a gift from the Dark Power.

Here's good news: the description of "Werebears" (MM page 207) describes how werebears usually only infect their chosen companions or apprentices with werebear lycanthropy (and then spend time with them to help them control it). So there's precedent in the Monster Manual for characters choosing to accept the "curse" of lycanthropy as a gift.

Here's bad news: the "player characters as lycanthropes" sidebar (also MM page 207) says:

lf the character embraces the curse, his or her alignment becomes the one defined for the lycanthrope. The DM is free to decide that a change in alignment places the character under DM control until the curse of lycanthropy is removed.

All the sources I can find tell me that kenku are strongly chaotic creatures; wereravens are lawful good. This is a major alignment shift! Kenku might view this as akin to mind-control: yes, it's power, and that's great, but after you do this you wouldn't be you any more.

If a kenku embraced the change and became lawful good, it would be difficult for them to fit in to kenku society. Most kenku are mischievous tricksters and many are criminals, and a lawful good creature might not enjoy interacting with such creatures.

Here's how your DM should feel about a PC doing this: your DM should be very uncomfortable with a character embracing lycanthropy, simply because it's so powerful. Very few of the creatures your group fights will have magical or silvered weapons, so the lycanthrope will be essentially immune to those encounters. Flying also makes you immune to a broad class of encounters (ie, encounters with creatures who can't hit you while you're flying). If you do this, it becomes much more difficult for the DM to design an interesting encounter.

Of course each DM is different. Some DMs might be okay with having this happen, especially if it happens to the whole group at once; other DMs might follow the rules text above and convert the kenku PC into an NPC.

Think about worldbuilding: Leaving aside the question of kenku for a moment, there's an opportunity for worldbuilding here. If being a wereraven is really so great, why doesn't everybody do it?

Maybe everyone does do it, and your group periodically encounters villages that are 90% wereraven/werebear/weretiger/etc.

If not everybody does it, the DM should think about why that is. Maybe the wereraven alignment change is more than just being lawful good; maybe wereravens are fundamentally different (obsessed with shiny objects, opposed to hats) in a way that makes most villagers reluctant to embrace lycanthropy. Maybe villagers are superstitious and biased against wereravens. Maybe there's something else.

But remember: kenku can't read the Monster Manual. In practice, an NPC kenku considering this isn't going to say: "well, the weapon immunity is good, but the alignment change isn't compatible with my rogue skills..." Instead, the conversation will go: "Hey, if you let me bite you and infect you with this disease I'm carrying, you'll grow wings and be immune to weapons! Trust me, this will be great!" Kenku can't really know for sure what downside there might be for accepting this offer, and it's all going to come down to trust.

(And, note: the wereravens you're talking about are from Curse of Strahd, ie, Ravenloft. Ravenloft is absolutely dripping with things that will lure you in with offers of power and then turn you evil. A very learned PC might be able to identify that this particular offer of power doesn't come with crippling drawbacks -- but most PCs that are willing to accept this sort of bargain probably won't last long in the Ravenloft setting.)