First off, I wouldn't be able to be a boss in a video game so much as the tough story turning boss battle in the middle of the game, that gives the main cast an epiphany, and they turn on the people that drove them to kill me because they see that their original goal would have led to the destruction of the natural world. P.S. I come back a plant element summon later <3
P.S. I wrote this in the idea that its an rpg game. I also used final fantasy terminology.

A) Where does the battle take place?
A lush jungle with intoxicating aromas of tropical flowers. The surrounding trees are obscenely old and large covered in a light green mosh with tendril like leaves hanging off the branches like hair. All manner of exotic and fantastical flower,and plant surround a circular arena like clearing in the jungle. A gigantic peony rests underneath a tree at the opposite end of said clearing. Thats where I would be sitting menacingly with large thick leaves and vines supporting my peony throne. The ground is thick with long flowing grass that waves in the wind giving it a look of water. The wind blows leaves and blossoms' loose from the surrounding trees. The sun is also just starting to set giving the entire area a pinky orange tint.

B) What is the level's theme song?

Green Scream (Aulbath's theme from Darkstalkers)
[link]

C) What is your pre-battle speech?
The heroes emegre into my area from a small jungle path. My throne opens to reveal me sitting there.
"You've come a long way, all in the name of a terrible goal."
The cheery hyper character with the knife specialty throws a knife at me my vines swatting it out of the air before it hits me.
"How does it feel to know you are contributing to death of this planet?"
I summon vines around the necks and bodies of the heroes and pull them towards me. I touch the main heroes cheek gently. He winces away from me.
"Is it so important to you to support a government that seeks to destroy this beautiful place for their own selfish needs?"
I drop the heroes. They gasp for air. One by one they get up and take a battle stance.
"I see, well if that's the road you wish to take, so be it"
I stand and walk down vines that are forming stairs as I need them, my hair and costume flowing in the breeze. The sash i wear around my arms swirls around me and then just rests at my wrists defying gravity and the wind. I take my battle stance.
"But dont think I'm going to make this easy for you!"

D) What is the battle theme?

Ayla-Trance Rave Jungle
[link]
(totally random trance I found whilst searching for a good theme, i suppose this takes away from the evilness of a boss battle but I would just be a misunderstood boss I suppose trying to protect the earth or whatever...therefore, I can have some happy battle music)

E) What special powers would you use to fight your enemies?

Are you kidding me!? Chlorokinesis of course!
My sash would be used in a manner similar to Roses' from Street Fighter.
I would summon lots of vine attacks and plant based spells.
My ultra attack would be like a whole cinematic thing to. Its called "Natures tears". The wind would pick up and petals would blow violently past as I summon masses of vines and plants to charge the heroes and entangle them while continuously damaging them. I disappear in the vines and and petals then re-emerge on top of the wave of vines and blow a kiss towards the heroes creating a cloud of pink pollen that casts status effects similar to that of a Malboro (of final fantasy fame). I then wink at the heroes and all the vines crash together violently and disappear wounding the party severely.


F)When you are defeated, any dying words?

Breathing heavily, I peer at the party.
"You have know idea of the consequences of this do you?"
The party looks at me disdainfully.
"Destroying this jungle wont be enough for you're government, they will just destroy and kill more of mother nature until there is none left leaving them with nothing but their cold steel and concrete and inadvertently eliminating most if not all of their resources for food, water and even oxygen. The world will be plunged into turmoil and death will eventually claim every living thing."
I gesture to them to look into a spring that rests behind my peony throne, and it shows what the government would do should the heroes continue on their current path. This gives the majority of the group their epiphany. They walk towards me slowly. I look at them tears welling up in my eyes.
"I pray that, that never happens; but if you continue on your current path, without a doubt, it will."
I turn towards them and hold my hands to my chest and look down, my hair and clothes catching the breeze.
"I beg of you" A tear flows down my cheek and falls to the ground, it hits and a small flower sprouts up "Dont destroy this earth."
I collapse to my hands and knees. I caress my tear-born flower gently.
I fall over and when I hit the ground my body explodes into petals that blow around the heroes giving them each a special item that gives them each a nature based power (Flower, Wood, Sand, Plant, Water, Wind, and Rock)

G) Anything else we should know about this final battle? Secrets? Tips?
Well first off equip status effect protection spells and Armour as my physical attack casts auto poison. I also have a weakness to fire and ice, obviously as I am plant based but I have ridiculously high evasion so there is only a 5% chance of stealing it manually. The other way is to equip an item called "Flora's Plight" (a ring that when equipped with my "Petal Crown" gives a 80% bonus to your speed, hp, and luck stat) which can only be obtained by a side quest in my jungle level. (You have to solve a puzzle that's located far off the main course) In the battle my crown is attracted to it, giving you a 40% chance of stealing it, thus exposing my fire/ice weakness. This is hinted at by a nomad at the beginning of the jungle stage.
The other method is to put silence on me so i cant use magic, limiting me to my physical attacks which with proper spells and equipment only have minor damage. This essentially means you would have to spam "Attack" on me and heal as necessary until I die. But I do have excellent speed and stamina stats so your "thief" character would need to be front and center in order to whittle down my health. It would be a good idea to cast "haste" on him to.

I totally want to do concept art for this now!