Fight with the Corpse Flower

Our party went down a tomb of a slain lich following a trail of stench and necromantic energy that lingered around a broken wagon. No loot left in the wagons, no bodies, no horses, just this awful smell, blood and faint track left of what seemed to look like tentacles.

In the tomb itself we had to go through traps that were setting off under a tiniest of breaths. Walking down the long staircase we could sense this evil necromantic energy getting more dense with every step we made. 

End of our descend was marked with giant doors left slightly ajar. Green light spilling out of the slit made us feel uneasy, not even mentioning the horrid smell of rot. 

To avoid being noticed by whatever was residing inside - ranger cats "pass without trace" which makes our movements soundless, as she builds up courage to approach the door. Ornaments remind her of symbols she've seen before. Open palm cut off at the wrist holding an open eye - a symbol of Vecna, deity of dark magic.
She peeks in. Her eyes meet a view she wasn't ready for. Giant throne room filled with vines all stemming from a furthest end of the chamber - gigantic Corpse Flower. It's fleshy body throbs, and with it all of the thick vines around, all creating a net on the floor, climbing up the walls to the ceiling where many corpses are held. Half digested, bloody goo of bodies. Like half chued meatballs spit out onto the walls, all fed upon by the flower on the throne. Six pillars, three on each side, hold green magical lights illuminating poisonous clouds suspended in this thick rotten air. 

Quick planning makes us use an brief element of surprise we've been given by the fate which made this damn flower completely blind. Ranger's arrows and  Druid's darts pierce the throbbing belly like knives, followed by the blast of fire cast by the Sorceress.
For two or three seconds the flower opens showing a disturbing view -the Lich who once ruled this place, dead as they come - merged with the bulbous flower.
"More sacrifices!" He howls, and with him all of the corpses collected in the throne room.

Seen first time in action Rune Knight invokes a rune of protection, making her skin thicker than it already is. She dashes through the viney floor, one warhammer in each hand, charging at the Corpse flower who already notices their presence and is not wasting it's time. Vines spring up and attempt to stop her but she's determined to kill. She knows this enemy is capable of using the corpses as temporary allies, and she hopes all of them will focus on her, as she's the one attacking their only animator.
They even planned it, she drank a potion of protection against fire, hoping to survive a blow the Sorceress will cast towards the crowd of zombies protecting the Flower attacked by the Rune Knight. 

But this is not what happens.
Horrid abominations fall from the ceiling down to the floor, sticky and poisonous they dash towards the party at the back. Vines slash the air while the Druid call for his fay friends for help and a pack of wolves appear to surround the enemies.

Corpse Flower attempts to run from the danger by climbing the wall, it's already twenty-five feet up but what it didn't expects is to be grappled and pinned back down to the throne by quickly growing in size Rune Knight. Giant might flows through her as she draws both of her warhammers ready to drum life out of this abomination.

Full size scan in the attachments 🔥