Ancient Behemoth Spider

Web Walker. The spider ignores any movement restrictions imposed by webbing.

Spider Climb. The spider can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Web Sense. While in contact with a web, the spider knows the exact location of any other creature in contact with the same web.

Multiattack. The spider takes three attacks: one with its bite and two with its legs. The spider can replace a bite with its web.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 13 (2d8 + 4) piercing damage, and the target must make a Constitution saving throw. The target takes 27 (6d8) poison damage on a failed save and half as much on a success.

Leg. Melee Weapon Attack: +8 to hit, reach 10 ft, 1 target. Hit: 11 (2d6 + 4) slashing damage.

Web. Ranged Weapon Attack: +3 to hit, range 15/30 ft., 1 target. Hit: 5 (2d4) bludgeoning damage. On a hit, target must make a strength saving throw (dc 14) or be knocked prone and restrained. The target can repeat the saving throw on each of its turns.

Summons (Recharge 5-6). As a bonus action on its turn, the spider can sound a thunderous clicking message, coaxing out a single Giant Spider from each nest (personal system, you might want to disregard) in its domain. The giant spider will try to the best of its ability to reach and aid the Ancient Behemoth Spider. The new spiders enter in sharing the Ancient Behemoth Spider's initiative value.