The Pantheon of Hallownest is a challenge from a game called Hollow Knight where the player takes upon all the bosses in a row. If they ever die, they reset at boss 1. Which can be really painful since each attempt can take around 40 minutes. The thing is that all the bosses have been faced before except the final boss which is the hardest boss in the Pantheon, which means it's also the hardest in the game.
When the player starts, they will fight a couple bosses then have a bench are to get to max soul and HP. Plus being abme to change their charms for the next fights. These happen about every 5 bosses except for the first 5. If the player has completed 8 separate bindings on the previous 4 pantheons, the player can also get lifeblood mask which is bonus health so the soul can be used for other stuff instead of healing.
Each of the bosses order is a combination of the previous 4, with the first 30 bosses being in close accuracy to the first 3 pantheons. While the last 12 are not even close to being the same order.
Once the player reaches the end, they take upon the end. The final 2 bosses in the game. The pressure they feel is unreal. Knowing if they die, they gotta reset it all from boss 1. The battle starts with the first boss, if they beat it. The final boss, and the hardest one, begins. If they survive long enough and deliver the final blow, they join 1.6% of people who actually have beaten it.