doing some development on cycles 1 and 2/some world building stuff
first of all: locations. The Event when the novice ripped Noxa Krov in two and wiped most of their own being from existence had a VERY large and destructive impact on the surroundings. as in completely leveling the surroundings and gouging a crater into the ground, with a pretty significant radius and depth. this specifically is how the two halves that would eventually become null and nil ended up completely isolated- the null-half got sealed underground and the nil-half stayed on the surface
by the time nil settled enough to have a physical form, so much time had passed that there were trees growing in the crater. it's all monoculture growth- same type of trees, same age, because they were all manually planted around the same time post-Event. so nil grows up in this crater, and null lives underneath it. they both eventually move on because of the same event- the crater is flooded, making it unlivable both on the surface and underground (at least for null and nil)
the final confrontation between null and nil happens on the cliff surrounding the crater. nil is knocked into the floodwater and dies, and null is petrified on the cliff overlooking the crater marking where Noxa Krov was defeated.
Fane does not leave null's side. A temple + sanctuary is eventually built around them. it is called Rest No Longer. Fane is treated as a guardian spirit of the temple and the crater. so is null, but to a lesser extent considering he's made out rock at the time
Rasputin is one of many travelers who takes respite in Rest No Longer. he actually ends up befriending Fane, up until he fishes Nil's stinger out from the crater and discovers he can use it to kill eternal-aligned beings with it and harness their Coil for his own gain and power.
after Rasputin uses the stinger to ascend both himself and Gazer into dragonhood, the two go back to Rest No Longer with Rasputin planning on a ritual in involving Fane and the stature of Null that would theoretically let him cross into the eternal plain. Instead, gazer (who has been loathing Rasputin for a while at that point) murders Rasputin with the stinger, dumps his body in the crater, and gets the hell out of there because fane found out what was going on and was PISSED.
at some point (either at that confrontation or at a later point) fane gets his hands on nil's stinger, and is able to use it to un-petrify Null. They both leave Rest No Longer for good, and it falls into ruin.
with the corpses of nil and Rasputin rotting in the already really magically unstable crater, and with petrified Null no longer acting as an "anchor" for all the unwound coil in the area, something was created from the remains of dragons.
thats bo. Boghast comes into being, and the flooded crater slowly but surely settles into being a bog. Along with the trees, there's now a whole bunch of cranberry bushes growing. What's significant is that this is the only place in the entire coil where cranberries can grow, and they're chock full of pure Coil.
most only know about the bog from rumors, as it's the sort of place where most who go poking around don't make it out the other side completely intact.
Boghast is vicious and territorial, and will attack and kill any intruders to the bog. however, anyone who is killed in the bog is eventually brought back as a revenant or ghost. or at the minumum the stuff their soul is made of is recycled into a new, technically-undead being.
so in short, boghast's bog is a mass graveyard. it just so happens that some of the residents are a bit more mobile than the rest