Giant Wolf Spider

A giant wolf spider on the party's side needs a hook. A druid or ranger befriended the pack. Animal Friendship or sustained feeding produces a creature that follows the party for a few sessions. It's not a pet. It's a wild predator that decided this group is part of its hunting territory.

Use the spider as a scout. Stealth +7, climb 40 feet, Darkvision 60 feet, Blindsight 10 feet make it a perfect dungeon advance party. Send it ahead to climb a vantage, and relay what it sees through Speak With Animals. In combat, the spider strikes opportunistically against already-engaged enemies. 11 HP and Bite at +5 for 1d4+3 plus 2d4 poison means it dies in a focused fight. Use it for flanking and drawing one opportunity attack per round away from a wounded ally.

The relationship has a timer. The first time the party leaves the spider's territory, it doesn't follow. The first time food runs scarce, it eats a horse. Plan the parting and make it hurt.

The druid has a name for the spider that no other party member likes hearing. That's the right feel.

A giant wolf spider is a CR 1/4 ambush predator with 11 HP, AC 13, Bite at +5 for 1d4+3 piercing plus 2d4 poison, Spider Climb, Stealth +7, and Blindsight 10 feet. It doesn't spin webs. It hunts on foot at 40 feet walk and 40 feet climb, sees in darkness out to 60 feet. The party won't notice it until it strikes.

Lead with positioning. Place the spider on a ceiling or wall before combat starts. On initiative, it drops from above onto the back-line caster using climb speed to land safely. The spider then runs the room using walls and ceilings to stay out of melee reach, driving engagement toward whoever has the lowest AC. 11 HP and AC 13 mean it dies in one focused round. Every turn it spends not adjacent to a target wastes its Initiative.

Run them in pairs or threes. One is an inconvenience. Two is a fight. Three with terrain forces three-dimensional combat. Wolf spiders are Unaligned and flee when an ally dies and the math turns bad. They retreat to a tunnel mouth or the rafters. If the party doesn't pursue, the spiders return the next night during watch.

Use them as pacing reminders that the dungeon hunts at night and open bedrolls have consequences. Cut the torches before the spider drops. A party fighting blind against a creature with Darkvision learns to bring better light next session.