To reproduce: give Isaac 2 Daddy Longlegs and Gnawed Leaf, go to the Satan Boss Room, and sit there until the familiars do their job. Satan's first phase ends (with no sound effect, oddly) and the chest spawns then and there. I don't fully understand how this bug works; if Isaac deals any damage using his own tears, or if he deals damage with Orbitals, then the 2nd phase doesn't get skipped. the Spider Buddy familiar seems to disrupt it too. So only some familiars cause this.
The Fallen seems to make no difference here and can be damaged/killed in any manner.
To reproduce: give Isaac 2 Daddy Longlegs and Gnawed Leaf, go to the Satan Boss Room, and sit there until the familiars do their job. Satan's first phase ends (with no sound effect, oddly) and the chest spawns then and there. I don't fully understand how this bug works; if Isaac deals any damage using his own tears, or if he deals damage with Orbitals, then the 2nd phase doesn't get skipped. the Spider Buddy familiar seems to disrupt it too. So only some familiars cause this.
The Fallen seems to make no difference here and can be damaged/killed in any manner.