These are just few notes for myself. If they are any good for you then great!

Where you can find Reaper's Fear

Acquired from: Act V, Heart of the Fortress, Malthael (Drop rate is currently lower than intended.) Where to farm: Act V, Heart of the Fortress Used for: Reaper's Wraps, Wrists, Health globes restore 25–30% of your primary resource, 5 random magic properties (as opposed to the 8 properties according to Battle.net) Note: Malthael also drops the Recipe for Reaper's Wraps.

Useful links:

Legendary Crafting Materials - Drop locations & uses