Devil Fruits exist in a cycle of reincarnation; when a Devil Fruit user dies, their ability is reborn in a new fruit. Instead of growing from a plant, the ability simply regenerates inside another similar fruit which then transforms into the Devil Fruit in question. When this happens, the empowered fruit changes appearance. Some characteristics of a fruit’s transformation into a Devil Fruit include the distinct spiral patterns, a curly stem, and a color change.
Outside of Blackbeard’s yet undisclosed method in which he stole Whitebeard’s devil fruit, this is the only way to acquire a Devil Fruit’s power from another user:
1. Kill them.
2. Wait for their Devil Fruit to re-spawn.
3. Get the fruit.
So what changed in Chapter 1052?
We got to see for the first time, the plant-based powers of Green Bull. Combined with his condition of not having eaten in years, it’s obvious that he is a Plant-Plant Man who feeds via photosynthesis.
Green Bull’s job, before becoming an Admiral, was to assist Vegapunk and the World Government. His objective? Steal useful Devil Fruits for the World Government to use.
Due to his Plant-Plant Devil Fruit, he is able to automatically re-spawn a similar-looking fruit to that of his target and then kill them to obtain it. Likewise, he is also capable of detecting exactly in which tree a Devil Fruit has re-spawned.
Green Bull is in Wano not to fight the Alliance but simply to obtain valuable Devil Fruits for the World Government and/or Vegapunk to use:
Hawkins’ Paramecia Fruit
Orochi’s Mythical Zoan Fruit
Kaido’s Mythical Zoan and Big Mom’s Paramecia Devil Fruit if they died. Although I can totally imagine Green Bull finishing off Big Mom/Kaido in his intro to show us how strong he actually is.