Well, to start it was once exclusively recognized as being an ability based around that of the character Kakuzu, but has since been adapted into a broader recognition through the playerbase being allowed to adapt their own iterations of this same basis in their own characters. Earth Grudge Fear is less regarded as an element or ninjutsu and is more defined in the structure of the user's body, in that their form has become that of a series of stitched-together parts that are extensively intertwined by a series of dense, thread-like tendrils that manifest throughout the entirety of the user's body. These threads are under the user's control, allowing for them to freely manipulate and engage with their body in various liberties that would otherwise be seen as physically impossible for any ordinary individual, such as the separation of their limbs from the body and then to reattach them after the fact with no consequence, or to open up large chasms within the body only to be rethreaded shut after the fact with no indication of blood loss or harm to the user. This effectively converts the user into that of a "rag doll-like being" that is made for bodily interchangeability, such as the means to adapt new organs or limbs to the user's body from "other sources" on the fly, which effectively serves as a sort of "pseudo-immortality."
Of course the threads and their means of manipulating the body in various ways is significant by itself, yet they only serve as a basic foundation for what makes Earth Grudge Fear unique when compared to the reference of the hearts that can be incorporated into the user's body. At any given time, a user of this "style" is capable of having up to five hearts at a time (this includes their own), of which these hearts were often regarded to be obtained through "taking" them from other people that the user targets. In doing so, these hearts are brought to the user as being sources for the utilization of advanced elements that they would ordinarily otherwise not have access to, in which are often represented and defined by a series of "masks" that show up across the user's body. In doing so, they sacrifice the means of calling upon one of their basic five elements in exchange for this newfound ability, such as trading fire for lava, or water for ice. Of course the requirement isn't to change an element out that matches the advanced element in some way, but they serve as easy examples.
Apart from this, I'm honestly not too familiar with this field as it isn't exactly popularized to have many points of reference both within the series and the RP itself, so I will be glad to receive any additional tips and information regarding this subject.