Those are great ideas, I think they work really well. Sadism as a shard, that’s scary. Maybe a magic system similar to Hemalurgy, but instead of spiking them and then spiking another you kill them, and the more sadistically you kill them, the more power you gain.
A drawback would be it greatly affects your sanity, the more power you gain more insane you get. Insanity follows the lines of sadism of course, along with possible homicidal tendencies.
Many, many terrorists in this world.