Hi V2Blast, good post, I don't think we've brought attention to this yet. As far as I know, no Tomb of Annihilation creatures have pronunciations, they were released after the pronunciation guide was completed.
I can't speak for the developers but I imagine they might do another pass on recent material once a few more adventures/supplements are released.
Not sure I want to trust Matt’s pronunciation...”siggils” comes to mind :D
I see your point, but to my knowledge Matt's not picking the pronunciations, just speaking them into the mic - someone at WotC (I think I heard it was Chris Perkins) is making the decisions how things are officially said.
The original Welsh form of the name Gwenhwyfar, which seems to be cognate with the Irish name Findabair, can be translated as "The White Enchantress" or "The White Fay/Ghost", from Proto-Celtic *Windo- "white, fair, holy" + *sēbarā "magical being" (cognate with Old Irish síabair "a spectre, phantom, supernatural being [usually in pejorative sense]").
Some have suggested that the name may derive from Gwenhwy-fawr, or "Gwenhwy the Great", as a contrast to Gwenhwy-fach, or "Gwenhwy the less". Gwenhwyfach (also spelled Gwenhwyach) appears in Welsh literature as a sister of Gwenhwyfar, but Welsh scholars Melville Richards and Rachel Bromwich both dismiss this etymology (with Richards suggesting that Gwenhwyfach was a back-formation derived from an incorrect interpretation of Gwenwhy-far as Gwenhwy-fawr).
Also this is from an interview with R A Salvatore:
Salvatore explained that Guenhwyvar had always been a "she." Being a fan of Mary Stewart's Arthurian series, he decided to name her "Guenhwyvar" after Guenhwyfar, the Welsh version of the name for Jennifer or Guinevere.
So, the closest we can find is the Welsh pronunciation of the original spelling of the name, which you can find here.
Though, having listened to all of the official audiobooks as well, the pronunciation varies on those and Salvatore himself has pronounced her name differently in different interviews!
I haven't listened to "The Collected Stories, The Legend of Drizzt" yet though, where Salvatore apparently talks about Guen and some of the other characters.
Ok, if you say so. It just seems a bit strange. It feels like "Manes" is the plural and that the creature should actually be called "Mane". But I trust you. Just hope you see where I'm coming from.
The pronunciations come from WotC, the people who create everything. They get to decide how everything is pronounced. It might seem wrong for our reality, but we are talking about a fantasy setting here.