I am wondering…
GR´s Penance stare (black) deals % of damage that enemy dealt… does damage dealt to allies from Thanos Court death passive count toward this damage? Did anyone try? 
That would be pretty interesting situation - Ghost rider punishes enemy for actually helping him
It doesn’t work with dmg done by Carnage to his own teammates so Im pretty sure it will be the same in this case.
That doesn’t answer if it counts the damage court death does to the other team. Is it excluded because friendly fire isn’t counted or because passives aren’t counted. I would think the enemy damage counts but the friendly doesn’t.
I’ve tested a lot of different characters in my quest to make thanos black usable and so far
Spider woman and Elektra negate the damage (to themselves only) with their black abilities.
There’s is no other way to reduce damage at all. It may be possible to use marvel, hulk or xfdp to trigger damage induced passive but I’ve not checked yet.
The GR question can be answered thusly…yes the penance stare would take into account the damage caused by thanos however it would be applied to the person who caused it so you would have to attack your own thanos in order to apply that damage