Justice is a fan-made global mod.

What is the basis for this conclusion? If it's a living tree, it shouldn't consist of just one element (earth)...

I agree about the unicorn. But the logic for the Ent is simple. What are the options: Living creature (by default), undead (immediately no), demon (immediately no), mechanism, and elemental. Correct me if I forgot something.
Why not a living creature - because it's not made of blood and flesh, as stated in the description of the "Living creature" parameter. And it's strange that vampires suck birch sap and restore their health.
Why not a mechanism - because this creature was not created, but born.
Why an elemental - because the creature has a direct connection to the forces of nature, without being man-made. i.e., not a golem.
And regarding the element of the Ent - water and earth together create a tree.
I sincerely believe that gargoyles should be mechanisms, for the same reason.
And why do gremlins have two repairs instead of one? And sabotage also has two?