[splatxp]

Well, I know DianCecht slays Demon. That doesn't include Dievils Heavils Smokies or Foggies, but it might affect the "demon" that appears in level 4 treasure maps.
I'm not sure, I haven't tested it myself.
I think those are the only slays that work thus far, if the demon slaying even works. I'm looking forward to the day we can see gnomes, ogres, pixies, and angels running around!