Behemoth. Base size is Huge, but some instances can become Gargantuan (Gargantuan grants Advantage on all Attack rolls and Players roll at a Disadvantage).

Corrosive Sludge. Capable of leaking corrosive sludge from open wounds or pores which quickly eats away at organic material, but has almost no effect on inorganic matter. It smells very sweet and enticing, causing Living creatures not native to the Old Tunnels in particular to become hungry at a greatly increased rate while in close proximity. Pools or trails of this sludge can be found throughout the Old Tunnels. Extended exposure can cause hallucinations and delirium.

Multiattack. The fungus makes 1d4 Rotting Touch attacks.

Rotting Touch. Melee Attack: +5 to hit, reach 10 ft., one creature. Hit: 16 (3d8 +2) necrotic damage.

Rotting Crush. Melee Attack: +5 to hit, reach 10 ft., one creature. Hit: 16 (2d8 +2) necrotic damage. Target is grappled on successful roll, and takes 1d8 additional necrotic damage at the start of their turn.

Slash. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 20 (3d10 + 3) slashing damage. The Vileshroom Juggernaut attacks with its held improvised weapon.

Corrosive Expulsion (Recharge 6). The Vileshroom Juggernaut expels a large volume of corrosive bile from its mouth in a 10-foot cone. Each creature in that area must make a DC 17 Constitution saving throw, taking (3d8) Acid damage on a failed save, or half as much damage on a successful one.

Fungal Connection (Recharge 6).. The Vileshroom Juggernaut calls 1d6 Adult Vileshrooms to its aid, bellowing out a loud, eerie cry.

Defensive Mist. The Vileshroom Juggernaut sprays a fine mist of spores and acid to ward away aggressors who approach its Garden or try to attack it. This is always used as a deterrent before combat is initiated. All Creatures within 10 feet must make a DC 15 Constitution saving throw, taking (1d8) Acid damage on a failed save, half as much on a successful one.

Guardian's Call. When the Vileshroom Juggernaught drops below half HP, or loses more than 20 HP during a single turn, it is able to immediately use Fungal Connection as a free action at the start of the next turn, refreshing the recharge duration of Fungal Connection.

If the Vileshroom Juggernaut reaches 1/4 HP at the end of a turn, it instantly becomes the Vileshroom Juggernaut's turn, ignoring Initiative or turn order. If other Creatures are near a Garden, it will use a Defensive Mist which lingers for the rest of combat on the Garden (damage cannot be reduced via Saving Throws). It will then move so that no Garden is within 30 ft of it, and begin to glow brightly. All creatures within 30 ft of the Vileshroom Juggernaut must make a DC 20 Saving Throw (Consitution or Dexterity), taking (8d10) Acid damage on a failed save, or half as much damage on a successful one. All Creatures which fail the Saving Throw are also knocked prone and have their AC reduced by 10 (until they take an extended rest). Equipment will be damaged severely by this attack.

Foul Wound. If the Vileshroom Juggernaut takes Blunt, Piercing or Slashing damage, creatures within 3 feet must make a DC 15 Constitution saving throw, taking 7 (2d6) Acid damage on a failed save, and no damage on a successful one.

Wrathful Protector. The Vileshroom Juggernaut becomes enraged if its Garden is threatened, gaining +4 on ALL rolls while any non-allied Creature is within the Garden.

Unrelenting Vengeance. The Vileshroom Juggernaught gains an additional 15 movement and can double its movement as a bonus action to chase a Creature which has done considerable damage to its Garden or slain multiple Vileshrooms. The Vileshroom Juggernaught will NEVER stop pursuing that Creature, and gains +5 AC against attacks from all other creatures.