It.

So, in your example the conduit of Jimmy's Momento Mori's power is his own physical body, but the power itself is something that is supposed to belong to the Momento Mori. Does this mean that a Revenant can directly activate and wield the power possessed by their Momento Mori?

If so, how is that any different from the Revenant themselves possessing the power? And if not, are there delay issues with having the power you're trying to "use" be channeled through a separate entity possessing its own will and motives?