D&D 5E Rules question - Knight of the sword Demoralizing Strike vs creature immune to frightened

[JAMUMU]

My reading of RAW is that it doesn't have to make a save, since you don't ever have to save against conditions to which you are immune. That would also produce the logical result. Character attempts to frighten it. It is immune. No save needed. Next.

This is also my reading of it. But then, sometimes the irresistable force moves the immovable object. This is when bribing the DM comes into its own.

 

[ECMO3]

I think it should have been worded differently. I think it should be worded as follows:

Once per turn, when you hit a creature with a weapon attack roll, you can attempt to frighten that target. The target has disadvantage on its next attack and must make a Wisdom saving throw (DC equals 8 + your proficiency bonus + the ability modifier of the score increased by this feat). On a failed save, the target is also frightened of you until the end of your next turn.

I think the designers just thought that frightened causes disadvantage and just decided not to worry about it if the target failed the save and did not think through the mechanics. That is the only way I can reason through the ability and what it causes.

The example of someone that can't be frightened is probably the most common "wierd" effect, but it is not the only one.

On the flip side RAW if you can't be seen and use this against a target that can be frightened and it fails its save it is going to have no effect. So if you are say invisible and you use demoralizing strike the target is technically "frightened" but has no disadvantage if he fails his save ..... but if he makes his save he has disadvantage!

 

[Paul Farquhar]

The target must make a Wisdom saving throw

Must it?

From the rules: "You don’t normally decide to make a saving throw; you are forced to make one because your character or monster is at risk of harm."

Note that there are exceptions, usually noted in spell descriptions (e.g. Calm Emotions) where the target can choose to fail the save, generally because the effect is non-harmful to them.

I would rule that a creature that is immune to fear is not "at risk of harm" and therefore is not required to make a saving throw. Since they don't make the roll, they fail automatically, and there is no effect.