Few thoughts are more discouraging than remembering that the mine passages one is exploring have been overrun by bloated and carnivous arthropods.
CR2 Giant Centipede - Large Vermin6 HP33 Initiative+2 Speed-C40(8) AC16(T10,FF14) Bite+5(2d6+4+d6 dexterity DC14) SQ Darkvision, tremorsense Abilities17,15,12,-,10,2 Saves+6+4+2 Rewards - 400 souls, 5% chance humanity