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Interestingly enough, those guys seem to have been the actual Bosses, there were no other bosses after them, we swiftly cleaned the last floor of the dungeon and even carried out the trees we got, even the grass, the ground, and I cut down large chunks of ores growing underground too.
After stealing everything I could, I began to inspect things out as the rest of the party was celebrating by having another snack, this time they were eating roasted eel and catfish.
I wanted to see if I could find something like a Dungeon Core. I remember hearing from the Elders that there was a Dungeon Core, and depending on its mood, the monsters would be aggressive, more passive, or stronger or weaker, and this mood was also unpredictable.
I used my Dig and Mining Skill to dig through all the underground, constantly expanding my senses. At some point, I reached the spatial walls below and couldn't continue forward.
It was hopeless.
Check "The Protagnist's Sister Is Actually the Strongest"!