Bile Titan

Plated Limbs. Since the Bile Titan stands at a staggering 30ft. any attack that can't reach it's upper body, it has to target it's legs. These have a higher AC (20) and these take half damage from all types, except psychic, they are immune to that and the legs are never vulnerable to any damage. Further more, ranged attacks targeting the upper body may get disadvantage from the height difference.

Colossal Mark. The size, and relative constant linear speed makes it easy to target this bug with siege weapons. Any siege weapon, or a weapon that the GM deems have similar property deals double damage against this titanic bug.

Legendary Resistance (3/Day). If the Bile Titan fails a saving throw, it can choose to succeed instead.

Stomp. Melee Attack Roll: +13, reach 10 ft. Hit: 59 (8d12 + 7) Bludgeoning damage. The target has to succeed a DC 21 Constitution saving throw, or be stunned until the end of it's next turn.

Bile Spew(Recharge 5–6). The Bile Titan exhales bile in a 60-foot cone. Each creature in that area must make a DC 21 Dexterity or Constitution saving throw, taking 63 (18d6) Acid damage on a failed save, or half as much damage on a successful one.

Call Bug breach. The Bile Titan spews pheromones in to the air, attracting the hive to this location. All Terminids try to answer the call in a large area. On the next round, they start crawling out of the ground. It may take multiple rounds for all of them to crawl out.

The Bile Titan can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The bug regains spent legendary actions at the start of its turn.

My turn. The Bile Titan can take any of it's actions.

Recharge Bile (Costs 2 Actions). The Bile Titan instantly recharges it's "Bile Spew" ability.