Death Domain currently offers Phantasmal Killer as a level 4 spell (it actually doesn't, bugged). Kind of an odd choice as it's an illusion and not really related to death in a concrete way. Maybe Circle of Doom as a level 4 spell instead or Undeath to Death.
Heart Clutch is also a very cool spell but a bit underwhelming as you are stunning yourself to stun someone else. To make it a little more attractive perhaps for the duration of as long as you don't break concentration/move (or until the spell duration ends) it keeps rechecking the save each round. So essentially someone could pass a save one round, but you can continue to channel and they may fail a saving throw in a future round.