Hi, I am a new member in the forum and I only am able to post here.
So basically one day I was discussing with a friend of mine "why Greenbull doesn't need water? What is his Devil Fruit ability?"
First we thought about the powers of the other's admirals and we reach the conclusion that the powers were the Natural Powers:
Element - Akainu (Magma)
Light - Kizaru
Gravity - Fujitora
The power that I suggest was of him having the special Paremicia type of Devil Fruit (like luffy and Katakuri) that changed his body into Phytoplankton and that could be not only represent the last Natural force, but also the fact of him not needing water or food because of the Photosynthesis.
When my friend said that an Admiral being a plant is kind of boring, I started to joke about Greenbull creating the island that Usopp trained during time skip. But… When I started thinking about it...
If we think about it that island/plant have a similar effect of the bird cage used by Doflamingo, it traps the enemy in the center of the island right before eliminating them. That island being a secondary effect of Greenbull DV awakening power could explain the fact of being so worthy to study by Hercules. Not only that but if it is a consequence of a battle could explain the fact of Greenbull dissappear and going under the radar (kind of like the bankai of Hirako in Bleach, the power that can't see friend or foe is better not use).
Last though was that a plant power is something really good adding the gravity of Fujitora to push Sabo through his limits and unleash the Mera Mera powers to cause destruction enough to appear in the Big News.
My friend concluded the conversation saying that he still thinks that Greenbull have some nuclear DV powers, but that the usopp island part was funny... So... "put that theory in the Arlong Park" forum and here I am.
This was my presentation, nice to meet you all.