Biomass

Unholy spread. The Biomass spreads ooze 5ft in all directions from the current edge of its ooze pool and summons one Biomass Entity

Great Split. If the Biomass is healed or given extra hit points an entirely new biomass will come out of the old one dealing 3 bludgeoning damage to the old biomass. 

Hivemind. All attempts to commune telepathically with this biomass's minions and all the things this creature's minions experience are directed back to this creature.

Corrode Metal: Any nonmagical weapon made of metal that hits the ooze corrodes. After dealing damage, the weapon takes a permanent and cumulative -1 penalty to damage rolls. If its penalty drops to -5, the weapon is destroyed. Nonmagical ammunition made of metal that hits the ooze is destroyed after dealing damage.
The ooze can eat through 2-inch-thick, nonmagical metal in 1 round.

Bio-summoning. Summons a Biomass Entity for each time it has used Unholy spread

Poisonous grasp. Melee Weapon Attack: +3 to hit, anywhere in biomass., 1 target. Hit: 4 (1d6 + 1) [poison] damage. The opponent is grappled.(DC 13)

Blob launch. Ranged Weapon Attack: +3 to hit, range 120 ft., 1 target. Hit: 5 (1d8 + 3) [poison] damage.

Enter the description for how legendary actions work for your monster here.

Legendary Action Name (Costs # Actions). Enter the description for your legendary action.

Enter the description for how mythic actions work for your monster here.

Mythic Action Name (Costs # Actions). Enter the description for your mythic action.