Tempered State

The Tempered State is a mysterious phenomenon in monsters that heightens their aggression. Every large monster in Monster Hunter: World can be affected by the Tempered State (including Elder Dragons and Subspecies) except Great Jagras, Great Girros, Dodogama, Kulu-Ya-Ku and Tzitzi-Ya-Ku).

In-Game Mechanics
Tempered monsters have a darker translucent skin, they do more damage and they enter in rage state more often. Tempered monsters bounties can be unlocked by gathering traces of Tempered monsters during expeditions or any quests.

Practical Uses
Tempered monsters are necessary to get various types of items called Streamstones. Streamstone Shard, Streamstone and Gleaming Streamstone can be used to meld decorations, Gleaming Streamstones can also be used to unlock the limit of armor upgrades, allowing to increase their defense furthermore.

Sullied Streamstone and Shining Streamstone can be appraised and they are converted into Warrior's Streamstone or Hero's Streamstone. Warrior's and Hero's Streamstone are used to augment fully-upgraded weapons, augments are special final upgrades for a weapon and there are five available options: Attack, Affinity, Defense, Slot Upgrade and Health Regen. The amount of augments available depends by the weapon Rarity and Warrior's and Hero's Streamstones can be strictly used to agument a specific pair of weapons classes: Sword (Great Sword and Long Sword), Blade (Sword and Shield and Dual Blades), Hammer (Hammer and Hunting Horn), Lance (Lance and Gunlance), Axe (Switch Axe and Charge Blade), Shaft (Insect Glaive and Bow) and Ranged (Light Bowgun and Heavy Bowgun).

List of Tempered Material Sources
This is a rough list of each Tempered material's sources, based on the rewards of their respective quests.
 * Streamstone: Threat Lv1 Tempered Monsters. (Pukei-Pukei, Tobi-Kadachi, Barroth, Jyuratodus, Rathian, Pink Rathian, Anjanath, Paolumu and Radobaan)
 * Streamstone Shard: Threat Lv2 Tempered Monsters. (Rathalos, Azure Rathalos, Diablos, Black Diablos, Legiana, Odogaron, Lavasioth, Uragaan and Bazelgeuse)
 * Gleaming Streamstone: Threat Lv3 Tempered Monsters. (Kirin, Nergigante, Kushala Daora, Teostra and Vaal Hazak)
 * Warrior's Streamstone: (?)
 * Hero's Streamstone: (?)