The Giant Rafflesia is the giant live plant found in the Arboretum dungeon on all difficulties.
It can be very challenging to defeat as the other monsters tries to slow you down. It is advisable that the room must be cleared of all monsters before challenging the boss.
This boss has a multitude of tools capable for dealing with long-range and melee combat users.
For long-range users, the Giant Rafflesia knows how to limit their mobility (Bombarding Spores and Vine Walls). Throughout the battle, this boss will rain down poisonous spores that deals at least 400 - 750 poison damage. Being hit by the bombarding spores will also inflict stagger which may lead you to be vulnerable to other attacks from the monsters lurking around the boss room if you had not cleared them out first. The purple markers on the ground indicate where the bombarding spores will land. The darker the color is, the closer the bombs will impact allowing you time to escape the explosion.
At times, there may be green markers on the ground which will then follow up with green-colored spore bombs. If they land on the marker, a thorned patch of vines will rise up on top of the ground, inflicting damage and bleed if you come into contact. These thorn patch can be weeded out with a few attacks.
The Vine Wall attack comes out fast from the ground, creating a barrier of thorns that impede your movement. Coming into contact will inflict 600 damage and bleed. If you are caught within the Vine Wall attack, a simple dodge movement will allow you to escape.
For melee combat users, the Giant Rafflesia has a variety of attacks (Poison Fumigation, Swallow and Regurgitate and Vine Swiping). For the Poison Fumigation, the boss will cover the perimeter around him with a poisonous cloud of gas, inflicting 1600 poison damage and putting you under the status of poison. Swallow is basically what this boss does; grabs the player with it's tongue or vine and swallows him/her. This chewing attack deals 100 - 200 physical damage and can hit up to 10 times before it regurgitates; spitting them out across the room. Lastly is it's standard swiping attacks with it's claw-like vines.
Occassionally, the boss will exude of a cloud of poisonously gas in front of itself, dealing 400 - 600 poison damage. It's also a multi-hitting attack if one stays within the cloud of gas for too long.
The battle for this formidable boss is set in two phrases.
The first phrase, the boss only spews out Bombarding Spores and the occasional Vine Walls. During this phrase, it is advisable to clear the room of any monsters before dealing damage to the boss.
The second phrase of the battle occurs once the boss reaches 50% or below, upon which it will be immune to all damage for a few seconds. After coming out from it's immunity status, the Giant Rafflesia will unleash it's Poison Fumigation (when it happens, all close-range fighters must evacuate). From there, the boss will start throwing boulders at the player with it's vine. Each boulder deals upward of 1000 physical damage to those unlucky to get hit by the attack.
There's also a likely chance that the boss will enter immunity status again once it reaches 20% of it's health. This time, the boss will recover it's health back to 40%. (Happens once or twice throughout the battle).
It also will drop seeds to make Nephentes pet.