Clerics of Argynvost's Fallen Flame have been reborn from death by a burning vengeance that imbues them with the power of light. Their brush with death grants them physical resilience and mastery over spells that can revive their fallen comrades. 

The Order of the Silver Dragon was a heroic order of knights established by the dragon Argynvost. The order was dedicated to protecting the people of Barovia from evil. When Strahd pushed his war against his enemies into the valley of Barovia, the Order became involved in the war, eventually coming to fight against Strahd's forces. Eventually, they were overwhelmed by Strahd's forces. Argynvost was slain in his mansion, his body hacked to pieces, and his head taken back to Castle Ravenloft by Strahd Though he was slain, Argynvost's spirit also lingers on. The Order was eventually wiped out at Argynvostholt, but they soon thereafter were reanimated by its leader Horngaard's zealotry and hatred for Strahd. They are eternal enemies of Strahd von Zarovich, but their hatred and undead nature make them a danger to Barovia as a whole.

A small faction of the reanimated knights rejected Horngaard's zealotry, when it became clear their hatred for Strahd had pushed them so far as to be evil themselves. That faction, though Reborn in death, retains an element of their humanity and remains dedicated to the true ideals of the now-fallen Order of the Silver Dragon  - calling themselves the Fallen Flame. 

Undying Vengeance

When you are reduced to 0 hit points but not killed outright, you can drop to 1 hit point instead. You can’t use this feature again until you finish a long rest.

Light of Argynvost

Also at 1st level, you can interpose divine light between yourself and an attacking enemy. When you are attacked by a creature within 30 feet of you that you can see, you can use your reaction to impose disadvantage on the attack roll, causing light to flare before the attacker before it hits or misses. An attacker that can’t be blinded is immune to this feature.

You can use this feature a number of times equal to your Wisdom modifier (a minimum of once). You regain all expended uses when you finish a long rest.

Channel Divinity: Cauterize the Wounded

Starting at 2nd level, you can use your Channel Divinity to channel burning radiance through your body that can restore a number of hit points equal to three times your cleric level and deals radiant damage equal to three times your cleric level. Choose any creatures within 30 feet of you, including yourself, and divide the hit points and radiant damage among them. 

Fallen Light Domain Spells

Improved Light of Argynvost

Starting at 6th level, you can also use your Light of Argynvost feature when a creature that you can see within 30 feet of you attacks a creature other than you.

Potent Spellcasting

Starting at 8th level, you add your Wisdom modifier to the damage you deal with any cleric cantrip.

Avatar of Argynvost

Starting at 17th level, you can use your action to activate an aura of sunlight that lasts for 1 minute or until you dismiss it using another action. You emit bright light in a 60-foot radius and dim light 30 feet beyond that. Your enemies in the bright light have disadvantage on saving throws against any spell that deals fire or radiant damage.