Two of the new items coming in the next build allow you to sacrifice one demon to apply a modifier to another. Modifiers have existed prior to this, but were only generated randomly. Now you’ll be able to (when you find the appropriate item) exercise some control over them directly. 
Once you find one of the items (either a Silver Matrix, or, if you want to modify a unique demon, you’ll need a Gold Matrix) and use it, you first select a demon to sacrifice. The modifiers each potential sacrifice provides are shown:
Then, choose a demon to gain the modifier:
Next, you’ll be shown a preview of the result. It’s easy to back up a step or two to change the sacrifice and the target, so you can quickly review the various combinations and their previews:
Once you find a combination you like, press Enter on the preview screen to confirm and ta-da, you have a newly modified demon, complete with new abilities!:
This feature has taken longer to work on than I’d have liked, but I think the next build including these and the other 20 or so new items will be pretty exciting. I’ll keep everyone posted on progress. 
Happy holidays!
):
