In a Monster of the Week game I'm going to be running this weekend, I want to have a Deal with the Devil kind of encounter for my players. To do that, I'm considering making a custom move for a monster that lets the players gain some mechanical benefit (I'm thinking a Move from any playbook, or solving some existing problem), if they are willing to mark off 1 point of luck from their character.
I want to make sure before I do this, though, that this is keeping in spirit with the way luck is used in these games. There's no moves in the rules that let the players spend their luck. I've never actually run/played MotW before, either, so I'm worried this might make luck feel like it's a little more in my control, rather than entirely theirs.
So my question is, would a custom move along those lines make Luck feel radically different from the base rules?