User blog comment:Kogath/Monster Hunter: World Discussion/@comment-6050823-20180605052242

Here's some more information that was revealed during the last two Monster Hunter Championships 2018 streams (1, 2), as well some information from some interviews ([1 http://dengekionline.com/elem/000/001/721/1721574/], [2 http://dengekionline.com/elem/000/001/721/1721560/]).

Rotten Vale
 * The top of the Rotten Vale is filled with piles of bones, plants, etc. that have accumulated together over time. Two giant skeletons belonging to giant monsters can also be found at the top of the Rotten Vale, acting as the foundation for the area.
 * They simply say that the skeletons belong to 'giant monsters', they never mention Dalamadur's name in the stream.
 * The middle section of the Rotten Vale further decomposes materials that come from the top. This part of the Rotten Vale is filled with the deadly effluvium, a bacteria that devours organic matter, that can make monsters aggressive by simply breathing it in.
 * The very bottom of the Rotten Vale is filled with what seems to be glowing blue water, but it is actually a type of acid that melts just about anything that falls in it.
 * Before anyone brings up Dalamadur I want to mention that the water from the Speartip Crag is simply from hot springs in the area, while the blue liquid in the Rotten Vale is acid.

Odogaron
 * Odogaron is constantly on the hunt for corpses in the Rotten Vale, competing with other species for the best ones, and is known to drag them back to its lair to feed on later.
 * Eating meat causes Odogaron's metabolism to increase drastically, making it faster and more aggressive, as well as causing its back to give off an eerie glow.
 * Like cats, Odogaron's claws are retractable. When it isn't hunting or attacking, Odogaron keeps its other six claws hidden until they are needed. These extra six claws have three rows of spikes on them, allowing it to leave deep cuts in prey, and to run at high speeds.

Vaal Hazak
 * It's theorized by researchers that Vaal Hazak was a predator in the past that fed on corpses filled with effluvium. It is believed that Vaal Hazak kept the bacteria with it for many years so that it could coexist with it in the Rotten Vale, thus allowing it to manipulate it.
 * Vaal Hazak doesn't directly prey on other monsters rather it uses the effluvium to do it. Vaal Hazak is known to suck up the effluvium so that it can make the bacteria's energy its own. When it takes it from infected monsters, it also drains the monsters of vital energy. Vaal Hazak doesn't kill the monsters when it sucks them dry but greatly weakens them, leaving the victims in a sort of unconscious state. By sucking up the effluvium, Vaal Hazak is able to energize itself without needing to prey on other creatures directly.

Elder's Recess
 * In early drafts, the Elder's Recess had powerful monsters from previous generations in it, before the development team chose which ones they wanted in MHW. From the beginning, the Elder's Recess was meant to be an area where powerful monsters attracted to the area's energy lived.
 * Upon dying in the Rotten Vale, the Elder Dragons dissolve in the effluvium, and their bioenergy accumulates in the earth before eventually crystallizing. This process made the crystals seen in the Elder's Recess. The ones in the center of the Rotten Vale have grown abnormally for unknown reasons.
 * Despite the appearance of the area, the Elder's Recess is a place filled with powerful monsters. Elder Dragons and other monsters, such as Uragaan, are known to gather there due to the immense bioenergy produced by the crystals in the area. Elder Dragons in particular nest there for that very reason.
 * The Elder's Recess has basalt filling some areas as well as some volcanic zones.

Gajalaka
 * Gajalaka are native to the Elder's Recess. Their village is within the Elder's Recess, however, they were driven out by Nergigante, which claimed their village as its nest. From Nergigante claiming their village, they were forced to travel to other areas in the New World.
 * This is the reason why we see the Gajalaka in a number of areas in High Rank.
 * Depending on the colored markings on their body, each Gajalaka will use certain weapons to fight. For example, Gajalaka with yellow markings will use paralyzing knives to immobilize threats. There are even "Snipers" among their ranks.
 * The Gajalaka design and decorate all sorts of masks for themselves, each with a different appearance, and choose their favorite one to wear.
 * The Gajalaka love fishing.
 * The Gajalaka were the first monster that Yuya Tokuda, the director of Monster Hunter: World, ever made.

Nergigante
 * Each Elder Dragon in the Monster Hunter series has their own unique characteristics. Nergigante's is its ability to cause massive destruction as well as to regenerate at an accelerated rate.
 * Since the beginning of the Elder Crossing, Nergigante has hunted Elder Dragons in the New World. Nergigante lives in the Elder's Recess because it was drawn there by other Elder Dragons that live within the area.
 * Nergigante hunts other Elder Dragons because of the large amounts of bioenergy within them. It prefers to eat prey that has large amounts of bioenergy.
 * During the events of MHW, Nergigante was waiting for Zorah Magdaros to die so that it could have an all you can eat buffet, but from hunters repelling the giant Elder Dragon, it didn't get its meal. From Nergigante not getting any piece of the Zorah Magdaros, it went on a rampage in the Elder's Recess, causing other Elder Dragons in the area to flee.
 * That's why Nergigante was nesting in the Elder's Recess.
 * The development team had a real hard-time designing Nergigante. Nergigante's design changed drastically over time, it went from gecko-like to a science fiction creature. Eventually, they went with designs that made Nergigante porcupine-like like the one we have now.
 * Nergigante doesn't mind injuring itself in battle since it can regenerate. When its spikes are broken, they regrow in near seconds, one at a time. Nergigante has about 1800, or more, spikes growing on its body alone.

Zorah Magdaros
 * After Zorah Magdaros was repelled, it died in the ocean, releasing an immense amount of bioenergy upon its death. It is believed that Zorah Madaros's bioenergy will create a new ecosystem in a couple of years.

Elder Crossing
 * Due to Elder Dragons going to the New World, the shape of the continent is constantly changed during each Elder Crossing from all the natural phenomena they cause at once. The map has to be updated consistently because the Elder Dragons always change the New World in some form when they appear. For example, when the First Fleet came to the New World the water levels were much higher than they are now due to some kind of Elder Dragon.
 * During the events of MHW, Zorah Magdaros made a path to the Coral Highlands by going through the Great Ravine. It also made a path that led to the Elder's Recess by passing through the Everstream.

Tempered Monsters
 * Tempered Monsters are old, experienced monsters that have been living in the New World for a long time. From them living in the New World for so long, these monsters have gained the bioenergy of Elder Dragons, thus making them stronger.

Elderseal
 * Elderseals are used to temporarily seal the powers of Elder Dragons.
 * That's all they'll say about the Elderseal, they don't want to give it an explanation beyond the one I mentioned above.
 * The development team added it as a new element for players, and also because it matches the narrative of the game's story for the Research Commission.