Tiny beast, Spider, Chaotic Neutral
"Calvin", as he's been dubbed by Captain River, is a typical wolf spider that is notorious for hanging around the guard barracks, much to the annoyance of many of the guards, but especially Alexander Greer. Many guards have tried to kill the little bugger, but he's extremely hard to hit. Given that he's not aggressive, most of the guards have now resolved to ignore him and hope that the sucker dies in the winter. This seems unhelpful, however, given that the spider has been around long enough to determine that this is likely not the same spider as the original Calvin.
Calvin is incredibly skittish and likely to flee at the first sign of trouble, preferring to hide when people are nearby. Druids, Rangers, and others with the Speak with Animals spell may attempt to coax him out of hiding (DC 10), but conversing with him reveals very little. His thought processes boil down to: "safe", "danger", "food", "nOT food", and very little else.
Survival. "Skitter skitter."
Run. "Skitter skitter."
Arachnid Stubborness. Any ability that requires a save from Calvin that does half damage on a successful save instead does no damage on a success and half damage on a failure.
Bite. Melee attack. +0 to hit, reach 5ft. Hit: 1d4 piercing damage.
Note: while he can bite, he will attempt to flee and hide if possible.
Calvin can take one legendary action per round (which is quite convenient for him, since he only has one choice). He may only do so at the end of another creature's turn.
Nuisance movement. He can move up to his base speed, if physically possible for him to do so.
Calvin usually hangs out around the guard barracks and gain benefits whilst inside. Despite Dolion's orders, there are typically many clumps of dust, cobwebs, and dark spaces in the barracks, making it an ideal place for such a spider. He may take one lair action every round on initiative 0 (wins initiative ties) while in the guard barracks.
Camouflage. While located more than 10 ft. from a creature, he may hide as though heavily obscured.