I'd give a +1 rebate for the IoP
Maybe another for the physical immunity(if he always carries it on him), since the source of his catch is always 'readily available' if you know about it.
Kind of like Nic's noose.
I haven't watched Once Upon a Time but, certainly, no magical dagger appears in the fairy tale. Is there some kind of connection made between the two stories?
Hi, thanks for the reply. I've included my responses in a spoiler tag below for those who do not want spoilers from the TV show Once Upon A Time.
There's not a ton of connection between the fairy tale and the TV show Once Upon A Time, other than the character's namesake and the spinning of straw into gold. There isn't much to tell of the dagger other than what's listed under Item of Power and The Catch. To put it in Dresden terms, "The Dark One" is a mantle of power. The dagger displays the current Dark One's name on the blade, in the case of the show OUAT that name is Rumpelstiltskin. You have crazy amounts of power and are unkillable except by the dagger itself. However, if someone kills you with said dagger the mantle of "The Dark One" passes on to that person. (i.e. In the show Rumpelstiltskin was the name of a man. He killed the previous Dark One and took on the mantle to become the creature of legend.)
The reason he doesn't get the +1 rebate for the Item of Power (dagger) is he purposefully never has it on him. He usually keeps it locked away or hidden, or on some occasions (later in the show) entrusts it to others for safekeeping. I may add +1 for The Catch simply due to the fact that if he were implemented into the Dresdenverse I'm sure any decent Wizard's library (or Bob) could point out the connection to the dagger.
Spoiler-Free / tl;dr
No IoP rebate due to not keeping the dagger on his person, but rather hidden away. And I may change the rebate to +1 for The Catch since the dagger link could be discovered by a good Wizard's library (or Bob lol).
EDIT: Anyone have any ideas on summoning him based on his name? Not his True Name, but just like how you may call Mab by chanting her name three times. This works with fae in the Dresden Files, but as I've built the character to be a human with a mantle of power like the TV show (not a Sidhe) I'm not sure how that works. Obviously one could use a ritual circle, and attempt summoning/binding, but I more so mean just randomly trying to summon him by calling out to him. This is done a lot in the TV show, people call to him and he appears.