Traditionally, the Faith Healer is a Doctor with a 50% chance of success.
On chatmafia.net, a Faith Healer isn't a percentage role. Instead, it reverses the protection on the target. If the target isn't protected, the Faith Healer protects them from a single kill. If the target is protected by someone else, that protection is undone.
A combination of the two versions is notably seen in the Open setup Faith Plus One.