Lumideer
Found in deep dark caves lit with bioluminescent species of mushroom which also their main diet,along with hanging mosses and tough roots which they use their tusks to dig up.
The water is heavy with minerals and calcium which gives them more nutrition.the added calcium does have a side effect with boney spines along the backs and males can have overgrowth on their antlers which can become too heavy for the stag to carry, the antlers often become stuck once they grow out of control leading to the male starving to death.
The bioluminescent mushroom causes parts of their body to glow which helps to blend them within the caves.
they have larger than normal ears with tufts as their hearing is accute where as their eyesight is poor, often they can only sense extreme brightness so they are almost blind. on their front legs are a curved sharp spike used for forging and digging at the harden ground but males can hook them into each other during fighting or into a female to keep her from fleeing.
They live in small herds and cannot survive for long above ground with the harsh light and louder sounds causing the animal to panic and injure itself.

crappy name for them but im always bad with names x3 background is from dear esther game on steam which is a slow paced and basic game but has stunning views and while wondering around in the glowly dark caves, thought of some small strange deer that could live down there.