That was all the information that applies equally to all players. However, of the ten thousand and nine players participating in the beta test of The Decagon, the game they did not realize was a game that contained a hidden feature until it was already far too late for them to do anything about it. They were fully trapped within this game that at least was not a death game... for those who merely remained just players.
The Decagon did become a death game to the nine players that were randomly chosen to become the nine demons, however. This game was now a death game to them, as they were the only nine players who were able to actually die within this game. They were not immortal within the game world itself, as their player character could just almost instantly re-spawn with a low cooldown mechanic. Nor were they actually physically invulnerable like all players were in the reality segment of The Decagon. The nine demons were truly and fully maxed out on everything and anything they could ever have wanted, with the difference between them and other players being that. They were like this both within and without the game itself, as they might not have access to magic and skill in what is now currently their 'reality'. However, what they do have is their base max stats, so while players are physically invulnerable to all damage that they take, a demon player is actually taking that damage; it is just that it takes so little of their HP(Hit/Health Points) that it barely moves from what it currently would be.
Although the massive difference between a player and a demon is that the player's HP does not change at all. They still feel the pain and everything else that would have come with that, whatever happened. They merely have physical invulnerability that does not say anything about what happens to them mentally. Pain itself is not truly physical only, as there is a mental aspect to the pain as well, and that was not removed. That aspect of it still happens, and the idea of players being physically invulnerable when in the 'reality' segment of The Deacgon was to make so that demons were not that easily spotted, as one wrong move and they could automatically be spotted and singled out. Also, they were given merely their max stats outside of the game world to prevent them from killing themselves via accident or on purpose after all.
While the players were tasked with killing all nine demons to finish the game, the demons themselves were given a task to finish the game as well, which was only for them, thus no normal player knows it at all. That goal was to kill all ten thousand players, which was something that was considered just as hard as the player's goal. They had to take out basically nine endgame superbosses after all, without any assistance, and create everything they needed on their own. However, in contrast, the demon had to take out all ten thousand players and lower their count to zero, something that seems doable given that they had maxed out everything.
However, numerous problems were unique to the demons that prevented them from easily achieving this goal.
1.
They were neither immortal in the game nor physically invulnerable outside in 'reality' themselves. They merely had an astounding, insanely high amount of HP to them that was shared between both layers of The Decagon. One trillion HP was what they were starting with, and their own attacks only do one HP of damage to themselves. Thus, if a demon did decide to try and kill themselves, it would take them over sixteen billion minutes, over two hundred million hours, over elven billion days, and over thirty one thousand years. For comparison, one million seconds is about eleven and a half days, and one billion seconds is nearly thirty one years. They would have damaged themselves longer than modern day humans have existed almost. The players can not do so themselves currently, either, as if they are not allowed to develop themselves over time. Even if one demon allowed all the current ten thousand players to attack them, it would still take all of them over one hundred million seconds to actually kill them this way, as their attacks currently only do one HP of damage to them. For nearly two hundred years, however, even that is not possible, as the starting areas only have a thousand players piece and there are ten of them. On top of that, they have killed nine demons, not just one alone. The environment, at least in the game world, might not have any NPCs at all, but it is still full of things that could cause environmental kills, but those would not work, as they also only cause one HP as well.
2.
They were not together at all. Unlike the one thousand players that each started off in the ten starting areas, they were not so lucky. That was the reason why there was always one extra player randomly placed in one of the ten areas. The extra ninth player of each of those chosen starting areas was picked as one of the nine demons. This was not going to be the nine players who were chosen last to fill up the ten thousand nine quota for the beta test. They could not just assume that those players were automatically the demons. That is not how the selection process took place, as all the players plus the one were equally split among the nine of the ten areas. Thus, it did not matter the order in which you joined the beta test in, as the selection process was done randomly for those in the starting area. Thus, a player who joined with single, double, triple, and quadruple digit numbers could be a demon, as there is no way for the players to know this. Also, the demons themselves do not know who the other demons are either. All nine demons are unaware of who the other eight are themselves unless they discover it, just like every other player. They only know the true face of one demon, themselves, and that is it. They can trust another demon, but nothing is stopping them from selling them out after all. Neither the players nor the demons were a unified front.
The next two are the really unique ones tailored just towards the demons themselves. Created with them in mind and not the players so much.