Rift Guardians In Diablo III:
Rift Guardian Bosses show up once the player’s advancement bar has achieved 100%. In order to get it to 100% you need to kill Blue Elites and Champions which are in Yellow. They will drop 3 yellow orbs for you to collect to get the bar to completed.
Whenever you finish a Rift Guardian they will drop certain key loots like Greater Rift Key, sometimes legendary item, and Blood Shards which are in purple.
Blood Shards: Special type of money you use to purchase high rare items, the higher the Torment level the higher loot drop on Blood Shards.
Crafting Material was added to replace just getting Veil Crystals, Reusable Parts, Arcane Dusts, and Death Breaths. Now you need to get certain crafting materials from each of the Acts in Adventure Mode.
A guaranteed drop for Greater Rift Keystone is only on Torment 6 anything below is 50%/50% on the drop rate.
Adventure Bounties played on Torment 6 is also the same guaranteed drops plus getting Blood Shards well as the crafting material for that acted
As of patch 2.4.1 here is the updated Rift Guardian list below.
Agnidox (engaged Demonic Hellflyer)
Blighter (engaged Herald of Pestilence)
Bloodmaw (engaged Executioner)
Bone Warlock (engaged Skeletal Summoner)
Frosty spell (enabled Izual)
Crusader King (engaged Skeleton King)
Ash (enabled Morlu Caster)
Erethon (engaged Corrupted Angel)
Eskandiel (engaged Corpse Raiser)
Hamelin (engaged Rat King)
Diabolical Maiden (enabled Fire Maiden)
Josh Mosqueira (engaged Punisher)
Master of Bells (easter egg, a reference to the Cow King, just shows up toward the end of the fracture named Infernal Bovine)
Man Carver (enabled Butcher)
Orlash (enabled Terror Demon)
Destruction (engaged Rakanoth)
Perendi (enabled Mallet Lord)
Raiziel (enabled Exarch)
Rime (enabled Xah’Rith the Keywarden)
Sand Shaper (enabled Zoltun Kulle)
Saxtris (enabled Deceiver)
Stonesinger (enabled Sand Dweller)
Tethrys (enabled Succubus)
The Binder (enabled Cydaea)
The Choker (enabled Barbed Lurker)
The Cow Princess (variation of the Lord of Bells)
Ravenousness (engaged Ghom)