Originally I wanted the grim reaper to join one of my households but when I learned he couldn't woohoo/date/kiss without losing his special effects I was heart broken. These sims are quite similar to their patron, Death. I am actively working on a version of the trait that is a selectable lifetime reward however I'm uncertain how long it will take. I personally still use it because it's quite handy. Your sim should now have the trait assigned to them, you do not need to keep clown's mod installed after you assign the trait. Scroll down the list until you see Reaper then select it. Select the 'Cheat Sim Info.' bubble then select the 'Add Trait.' bubble.

You'll need to install the mod listed above then shift+left click the sim whom you want to assign the trait to. If you're using the (Hidden) version of the trait you'll need to assign the trait manually. It requires the use of Clown's mod located here > Reaper (Hidden): Is a very quick and dirty fix for those who want only a few select sims with the trait and not a whole town. Be warned townies can be assigned this trait so you might see some randomly generated reapers. Reaper's Apathy will occur more often and also had it's emotional intensity increased. Reaper (Updated): Is the updated version of the trait. Added an additional flavor of the trait and buffed Reaper's Apathy to actually be more of a nuisance.