The bossfight was against Malus Thorm. I convinced him to battle royale his sisters to death and then engaged him in combat. Asterion talked to him while the rest waited in the shadows hidden so we could get the jump on him.
Shadowheart
Helmet - Wapira's crown. When healing another, heal 1-6 hp up yourself.
Shoulders - None.
Chest - Non-magical half-plate armour.
Gloves - Herbalist's gloves. When the wielder heals a poisoined creature, it is no longer poisened.
Feet - Vital conduit boots - When the weareer costs a spell that requires concentration, they gain 8 temporary hit points. Atheltics +1.
Weapon - Defender flail - Reduce incoming bludgeoning, slashing and piercing damage by 1, Weapon enchantment +1, AC+1, Tenacity, when missing do 1 damage regardless.
Off hand - Shield of scorching reprisal - Shield bash ability, Resistance to fire damage, Blazing retalliation ability.
Necklade - The spectator's eyes - nice necklace that gives 2 single use spells per day.
Ring 1 - Ring of mental Inhibition - When a foe fails a save vs one of your spells or attacks it gains a debuff that lowers his save values for WIS, INT and CHA for 2 turns. Debuff is 1 per turn remaining on the item.
Ring 2 - The sparkwall - grants resistance to lightning damage. Wielder cant be electrocuted.
As you can see nothing here is triggered by other peoples healing the character. All the effects trigger on Shadowheart healing others. Overall the rest was to make her tanky as I noticed she was getting targetted alot in my early game.
These were the conditions on her prior to the fight:
Blessing of Selune - resistance to necrotic damage
Pixie blessing - the shadowcurse cannot effect this character. Gotten it by releasing a Pixie from a moonlantern.
Greater elixer of arcane cultivation - Additional lvl 2 spell slot. From an elixer.
Temporary hit points. Honestly though im not sure if she still had these when the event triggered, but it was there at the start of the fight. Think one of her effects proc'ed this earlier but I cant say what exacttly.
Lightly obscured. I was hiding with the party save for Asterion who I send forward to talk to the boss.
I also had 5 smmons in total in the fight. But they played no part in this. All included I had 2 Spiritual weapons (Maul) from Shadowheart and my MC, for Shadowheart the duplicate with still like.... 8 or 9 turns left. I had summoned the Quasit as I still had the scroll from early game and curious what it actually did. It was chilling in the back of room far away from the fight. He was invisible and not involved. Dident roll initiative even. And an Azer from Gale. Which had the attack that confused me just prior to the whole 'healing makes concentration dissapear' event.
Gear for my MC:
Helmet - Warped headband of Intellect. - Int was his dumpstat so I figured it would be a good fit for him
alsno noone else could really use it better so eh? No effect on healing though. Just a stat increase.
Shoulder - Ca;e lf the red prince. Only cosmetic to my knowledge. No ingame effects?
Chest - Breastplate+1 that I stole from the druid grove. Er.... I mean was gifted to me by Lathander. Yes defenitly!
Gloves - Gloves of belligerent skies. When doing thunder, lightning or radiant damage on an enemy also cast Reverberation on them. WHich is a stacking debuff that effects their saves. Not applicable to healing as it only is effected by damge.
Feet - Boots of striding - when you cast a concentration spell you gian momentum (speed buff) for 1 turn and while concentrating on a spell you cant be moved or knocked prone against your will. Athlethics +1.
Weapon - The Blood of Lathander. Nice fit for my cleric of Lathander id say
but no effect that triggers on healing as far as I can tell?
Off hand - Shield of devotion. +1 lvl 1 spell slot. Shield bash ability. Can cast aid once per day (which I always forget)... doesent seem to effect healing.
Necklace - Uncovered mysteries - allows me to cast detect thoughts. As I seem to have talk to the dead from other source already? Because of that I swapped out the necklace. Honestly no clue how I can cast it without the previous necklace though but its there....
Ring 1 - Caustic bandd - attacks gain +2 acid damage.
Ring 2 - Strange conduit ring - while concentrating on a spell the wearer's weapon attack do an additional 1D4 psychic damage.
Maybe the conditions effecting him then?:
Blessing of Selune - resistance to necrotic damage
Pixie blessing - the shadowcurse cannot effect this character. Gotten it by releasing a Pixie from a moonlantern.
Elixer of hill giant strength - sets STR to 21. Great helps smashing things
no effect on healing.
Speak with animals. - can talk to animals until next long rest. Nothing to do with healing.
Recast speak with the dead - Same as speak with animals. No oeffect on healing.
Lathander's light - effect from The Blood of Lathander. - emit light in 6 meter radius and undeads and fiends in that radius have to save vs con or be blinded. Incidentily, dont think ive seen one of them resist this effect? Do they get a roll? Not sure...
Hiding - Like I said this list is the effects from right before the fight. I was holding my people back until Asterion triggered the boss.
Clear area - hiding while your holding an artifact Mace from your god that emits light in 12 meters around you is apparently kinda counter-intuitive to hiding. Whoops! No effect on healing though
let me know if the video is needed or wanted. I also got a save from like.... 2 meters away before I triggered the fight in case that helps with reproducing things?