Monster Hunter

What we know

Outsider specialists who hunt monsters and oppose Strahd von Zarovich in Barovia (Session 4 @ 02:02:58)
Dr. Rudolph van Richten famous among locals; copies of his Monster Hunting Guide circulate in the valley (Session 6 @ 00:59:22)
Ezmerelda d'Avenir identified as a monster hunter at Khazan's Wizard Tower (Session 14 @ 00:16:53)
Not a formal guild—Dr. Rudolph van Richten works alone per Ezmerelda d'Avenir (Session 14 @ 00:32:30)
Nightingale operates as independent vigilante ally; partners with van Richten's alter ego V (Session 17 @ 21:55)
Confirmed as Urwin Martikov's friendly blue-bird-logo street acrobat (Session 13 @ 00:25:59; Session 16 @ 01:49:14)
V confirmed as Urwin's gruff lone investigator = Dr. Rudolph van Richten (Session 12 @ 02:59:10; Session 18 @ 02:27:19)
Father Bryce and V are van Richten aliases; Nightingale is a separate ally—party knows Bryce and Nightingale are distinct individuals (Session 17 @ 19:38)

Dr. Rudolph van Richten — famed vampire hunter; aliases Father Bryce and V; author of monster-hunting publications; failed Castle Ravenloft revolt (Session 4 @ 02:02:58; Session 18 @ 02:27:19)
Nightingale — vigilante codename; Court of Wolves investigator; van Richten ally; true identity unknown under mask (Session 13 @ 03:24:14; Session 17 @ 19:38)
Ezmerelda d'Avenir — Vistani monster hunter; van Richten's former protégé; hunts him in Barovia (Session 14 @ 00:32:30)

Session 12 alley: masked rescuer V killed Court assassin with silver dagger (Session 12 @ 02:59:10)
Party allied with Nightingale against Court of Wolves kidnappings (Session 16 @ 01:58:57)
Hideout debrief: Volenta identified as Court puppet-master; driving her out dismantled the false Court (Session 18 @ 02:14:56; Session 20 @ 00:25:22)
Ezmerelda d'Avenir de-escalated at tower; loaned silver weapons to party (Session 14 @ 00:28:52)

Unconfirmed: Nightingale's real name and face beneath the mask (Session 13 @ 03:24:14)
Unconfirmed: whether Rictavio is connected to Nightingale (Session 13 @ 00:25:59; Session 16 @ 01:49:14)
Unconfirmed: full relationship between Ezmerelda d'Avenir and Nightingale / Goldie (Session 14 @ 00:21:13)
Unconfirmed: whether other monster hunters operate in Barovia beyond these three (Session 14 @ 00:32:30)