Penance Stare: Ghost Rider deals penetrating damage to opposing characters that have damaged a friendly character since your last turn.

What exactly counts as an opposing character damaging my characters so I can use Penance Gaze?
An opposing character must directly cause one of your friendly characters to take damage. The most obvious example would be damage from an attack, though other damaging effects like Poison would work, too.

Indirect effects, where the damage just happens to occur as a result of something the characters did, would not work. For example, Incapacitate can cause a character to take pushing damage, but all Incap itself does (and, by extension, all the character using Incap is responisble for) is place a token on the target. Now maybe the target will take pushing damage from that token and maybe not... either way, the damage isn't caused by the attacking character. Another good example of indirect damage is knock back damage; an opposing character's attack (or other action) may cause your character to be knocked back, but the knock back damage comes not from the attacker but from the knock back path being ended prematurely.