Malphas is a demon in FAITH.
It's still unsure about Malphas existence and any information. It is currently unknown what Malphas does.
Father Garcia was desperately trying to discover the name of a powerful demon a cult was attempting to procure in a secluded area of Connecticut. One attempt in doing so was through exorcism of a boy, Michael Davies. This did not prove fruitful, however, as his possession proved to be unbreakable.
In the "best" ending of FAITH: Chapter II, Father Garcia addresses a letter to John Ward in which he states he was able to discover the name of the demon: Malphas. He explained that the cultists operating in the area are looking to use the twin Martin boys as a means of summoning this demon into their world. Asking John to prepare himself, Father Garcia stated that he was in the process of finding the location where this would occur.