There are so many original characters, creatures and concepts to cram in, and only so many existing cards that are a thematic fit
While there are cheaper options in mono-black like Raise Dead, Fell Horseman gets the edge in my opinion by also being a creature you can play later if needed
The Vindicate Test would therefore imply that value of Pack Rat is not in its efficiency, but in the ability to turn any card into a threat and the natural resiliency that comes from the cloning ability
Cards that dont targetlike Exsanguinate or Weftstalker Ardentstill affect you because they dont pick you as a target
Firstly its 4-colour identity (including the powerful blue) gives this deck lots of options to fill up the 99-cards in your Commander deck
That extra 5 sleeves means you have backup ready for lost cards, sideboard swaps, or double-sleeving your most precious foils