Giant Black Widow Spider
ATK 1 bite
DMG 1d6 + save or take additional 3d6 damage
Giant black widows lurk in the dark places of dungeons, spinning sticky webs throughout their layers. Anyone fighting in these webs take a -1 penalty to attack rolls due to getting caught on threads. They are ambush predators, and are unlikely to attack large groups of heavily armed adventurers, preferring to attack stragglers. The venom of giant black widows is valued by assassins. Giant black widows are around twice the size of a human being.
Giant Jumping Spider
ATK 1 bite
Unlike their black widow cousins, giant jumping spiders are active hunters, moving quickly through the halls of dungeons in packs. As their name suggests, they can jump very far, allowing them to close gaps rapidly. They have large, complex eyes, allowing them to see well in the dark. Giant jumping spiders are about the size of large dogs.
ATK 2 claws or 1 sting
DMG 1d6+1 each or 1d6+2 + save or take additional 3d6 damage
An ambush predator, like the black widow, giant scorpions often try to flatten themselves against a wall and pretend to be part of the scenery, keeping completely still. Their massive stingers move blindingly fast, and deliver a potent dose of venom. Giant scorpions are about the size of bears.
Giant Dungeon Shrimp
AC light + shield
ATK 1 claw
Shrimp are not particularly threatening, and neither are their giant air breathing cousins. Although slightly resembling giant scorpions, giant dungeon shrimp are significantly smaller, about the size of a human. They feed on decaying matter, fungus, and other dungeon detritus, only resorting to violence if desperately hungry, attacked first, or they simply have a good opportunity. Their exoskeletons are translucent, allowing full view of the organs within.
ATK 2 claws
DMG 1d6+1 each
The clickety clacketing of a giant crab's shell is enough to send hardened adventurers fleeing. Giant crabs are fierce, bear-sized predators that have no fear, with razor sharp claws and hideous clattering mouths. They taste quite good, however, and are considered a delicacy by many dungeoneers.
ATK 1 bite or sting
These colonial nightmares are both a dungeon delver's best and worst friend. On the one hand, the workers that make up the bulk of a colony are weak, and often carry treasure into convenient storage rooms that are ripe for raiding. On the other hand, when the colony is threatened, warrior ants will swiftly be sent to deal with intruders, and their stingers can melt prey from the inside out. Colonies usually have 1 or more queens constantly laying eggs, meaning that even after clearing most of a dungeon, it can be restocked with chitinous horrors within a few weeks. Worker ants are about the size of dogs, warriors and drones are the size of bears, and a queen is around the size of a hippopotamus.
Worker: HD 1, bite and sting 1d6, HDE 1
Warrior: HD 3, bite 1d6+1, sting 1d6 + save or take additional 3d6 damage, HDE 4
Reproductive Drone: HD 2, bite and sting 1d6+1, HDE 2
Queen: HD 5, bite and sting 1d6+2, HDE 5