How would you write an effect for old school Protection from Evil type?

[Nickademus]

Because the IFT statement is evaluated on outgoing attacks and not incoming?

It's not the IFT that he's referring to. It's the 'AC' tag. When a creature is attacked, FG looks through all the effects on that creature for modifiers to AC which seems to be the reverse of most of the effect tags which do something based on the one doing the action. In reality, FG looks through the effects twice in this situation: once on the attacking creature for effects that modify ATK or any relevant ability score or value, and again on the defending creature for effects that modify AC or any relevant ability score or value.