The character who posses the power of Rain God, Forest God and Earth God are Dragon, Aramaki and Blackbeard according to this theory.

SUMMARY

One Piece is written by Eiichiro Oda, who started penning this story in 1998 and has been going on ever since.
Luffy has the power of Sun God; aside from him, there is Rain God, Earth God, and Forest God in One Piece.
According to a theory, Monkey D. Dragon, Blackbeard, and Aramaki are the ones who have the power of gods in One Piece.

One Piece is the only manga ever that has managed to keep numerous mysteries unsolved even after 27 years. One of the most prominent reasons why One Piece managed to get ahead of its rivals is the ability of Oda sensei to keep the readers immersed in his story, surrounded by a myriad of mysteries.
One Piece Logo
One of the most ground-breaking revelations in One Piece happened when it was revealed that Luffy’s Devil Fruit was never the paramecia Gomu Gomu no Mi. Instead, it was Hito Hito no Mi Model: Sun God Nika. Now that we know the Sun God exists, there are other gods such as Rain God, Forest God, and Earth God hidden in the Grand Line, according to a theory.

3 more devil fruits gods are residing in the Grand Line in One Piece

The fact that we know so much about the One Piece world yet so little about its realities even after 27 years depicts the writing ability of Eiichiro Oda, who has solidified his place as the greatest manga writer ever.

Ever since the revelation that Luffy has the abilities of the Sun God Nika, fans have started wondering about other gods. There are only 4 known gods in the One Piece universe. They are the Sun God, the Rain God, the Forest God, and the Earth God.

Since Luffy has the power of the Sun God, that leaves three more gods who are yet to be revealed in the story. However, we do know that the gods are in a different realm as compared to others.

Luffy in Gear 5 in One Piece
According to the World Government, the Sun God Nika fruit grants the most ridiculous powers of any Devil Fruit and gives its user rubber-like properties as well as cartoon physics. Luffy has just unlocked his true powers and yet there are numerous aspects of his power yet to be revealed. 

One theory gaining popularity among One Piece fans states that the Rain God power is bestowed upon Luffy’s father, Monkey D. Dragon. While the Forest God powers are speculated to be in the possession of Navy Admiral Aramaki. 

Last but not least, according to the theory, the most likely character to possess the abilities of the Earth God is Blackbeard.

Other gods in One Piece aside from the Sun God

The theory making the rounds among the One Piece community states that Luffy’s father, Monkey D. Dragon, might be One Piece’s God of Rain. This theory is based on the instance where, when Dragon used his power, the weather in the area became stormy, with rain, great winds, and lightning strikes occurring.
Monkey D. Dragon rescues Luffy in Loguetown.
However, we don’t know much about Dragon except that he is the leader of the Revolutionary Army and the most wanted criminal in the One Piece world. The next character who is rumored to have the power of the Earth God is Blackbeard.

The theory states that ever since the introduction of Blackbeard, it has been mentioned numerous times about the parallels between him and Luffy. Although their end goal of becoming the King of Pirates is the same, their approach is vastly different.
Blackbeard’s Dark-Dark Fruit from One Piece
Since the Sun God stood for freedom, the Earth God would represent the opposite, as they are farthest from each other metaphorically.

The only character in this theory who has shown evidence of having the power of the Forest God is Navy Admiral Aramaki. He has the power to transform himself into plant life, and create and control it as per his will.

Aramaki from One Piece
He was shown to suck power and life energy out of his opponents by attaching them with roots; this makes him the prime candidate for having the Forest God power.