Yeah, like I said before, something like near death. Body parts, specifically the torso and/or the head have to be at the red. Being unhealthy could work, or alternatively being healthy would make sense for the body to fight the blob as it’s trying to take over in the character’s near death state. Having some radiation might work, like some sort of trigger to get the blob and the body mutating. Heck, perhaps even the spiritual state could have some effect - much like how having cannibalism alongside boosts morale more with the trait on, some sort of thing… like the mind being more welcoming through this strange rebirth of sorts, if that makes any sense.
Instead of the blob taking over and the character becoming completely changed, something like your human self, still being alive but near death, resisted the blob’s takeover in your vulnerable state. However, that interaction has somehow merged your consciousness with whatever the blob is. You’re yourself, but not quite, and you’re not quite like all the other zombies either. Some sort of anomaly.