Zblrg would have been among the first to agree that Hell was an awful place. It was, after all, filled with awful people. Also, quite a few demons, which was nearly as bad.
Quite a lot of demons, actually - certainly more than were needed to torment the population of the damned. Very few souls warranted individual attention, and some torments didn't even require a demon to be present. The largest and most powerful demons could pretty much handle everything themselves, and that left a lot of weaker imps with nothing much to do but watch, wave pitchforks, and cackle - and wow, that got boring fast.
Imps could look for something to do that had nothing to do with tormenting souls, but there weren't a lot of options. You could look at rocks, or molten rock, or ice, but these were all barely more interesting than the suffering damned. You could find a relatively quiet corner of Hell and play board games, but since this was Hell the only games available were Monopoly and Candyland, and that made the idea of waving a pitchfork and cackling for all of eternity seem a lot more appealing.
So when the invasion came along, at first Zblrg felt as if its prayers had been answered - metaphorically speaking, of course.
It wasn't immediately obvious that it was an invasion. Initially it was just a mysterious sphere of darkness about the size of Zblrg's head, floating about three feet off the ground, but even that was new and interesting enough that Zblrg immediately sold both of its railroads and all three green properties to its fellow imp Flmgr for a dollar, grabbed its pitchfork, and scuttled off to investigate. Kgmfl, who had been winning until this sudden reversal, howled in rage.
For a long time, the orb of darkness just sat there and did absolutely nothing, and yet it was still the most interesting thing that Zblrg had ever seen. Zblrg got very excited when the orb suddenly expanded in size until it was taller than Zblrg was. When it started spitting out various probes and small animals in cages and such, Zblrg waved its pitchfork and cackled with glee in spite of itself.
By this point, Flmgr had successfully bankrupted the other demons from their game, and came over to see what all of the fuss was about. As such, it happened to be standing nearby when the humans stepped out of it.
Zblrg was simultaneously fascinated and horrified. These were actual humans made of meat and bones and things, not just disembodied souls. Flmgr either didn't realize exactly what was happening or was simply overwhelmed by enthusiasm, but it immediately leapt forward and brandished its pitchfork menacingly. One of the humans shot it.
Now, Zblrg knew perfectly well what a gun was, because every once in a while the denizens of Hell would learn about the human world when some enterprising diabolist summoned a demon there for a while, but it didn't expect bullets to actually do anything to a demon. Certainly they never did the diabolists any good. It was therefor extremely surprising that Flmgr just sort of disintegrated.
Up until this point, Zblrg had been absolutely certain of two things: that it would exist forever, and that it kind of wished maybe that wasn't the case, because existence sucked. However, faced suddenly with incontrovertible proof that eternal existence was not so certain after all, it was suddenly filled with an overpowering sense of self-preservation, and immediately dropped its pitchfork and raised its hands in the universal sign of "I'm totally not with that guy."
"Hah! The blessed ammunition worked even better than I thought it would! Riley owes me a hundred bucks," one of the humans said.
"Should we take a look around?" another human asked.
"At what? You think the rocks behind those rocks are going to look that much different than these rocks? Let's just get started," said yet another, the only one not holding a gun, Zblrg noticed.
"Isn't that a bit reckless?"
"Pfft, he who hesitates is lost. You think we're the only ones working on a project like this? No one cares about whoever comes in second," the apparent leader said. The subordinate shrugged and disappeared back into the bubble of darkness.
"Excuse me," said Zblrg, and the words felt distinctly odd on its tongue, "but are you scientists? Explorers?" It looked again at how many guns the humans were carrying. "Theologians?"
Before the man could answer, the sphere suddenly doubled in size, and then quickly doubled again. The next thing to emerge from inside it was a bulldozer.
"Real estate developers!" shouted the man over the sudden noise. "You're standing on the future site of the most cutting edge, exotically-located luxury apartments in human history!"
"Why would you possibly want to build apartments in Hell?" Zblrg asked.
The man gave Zblrg a pitying look.
"Do we look like people who could get into Heaven?"