… you don't necessarily have to kill a friendly peasant (or in Celeste, an Angel) just attacking, even unknowingly, will cause them all to go hostile.One game, I had Immolation cast on my party and went to Celeste. I was unwittingly attacking everyone in sight and of course, they all went ballistic (hostile) and began to attack my party.
I couldn't understand what happened. It took a little bit of searching to see the Immolation Spell icon was active. Luckily, I was able to load a previously saved game from before I entered Celeste fully loaded & on fire.