A literal Mighty Glacier (and even referred to as such), Masthemoth is introduced as a grouchy, anti-social, and easily annoyed woolly mammoth/mastodon kaiju, and literally the last elephant left on the surface world (the rest of them are currently in nature preservation centers in the Sky Kingdom). As such, his tendencies can generally be ascribed to loneliness, especially after thawing out of the glacier he had encased himself and his partner in centuries prior. The first kaiju he meets upon awakening, a short time prior to the beginning of "Fire and Ice", is the snarky Fire/Stone-type feline kaiju Beryleon, who is probably the polar opposite to the Ice/Earth-type mammoth in every way possible. Though they do butt heads initially (with one instance being an official KK match where Beryleon is all but reduced to sand grains), the events of that book eventually bring them extremely close, especially after their partners fall in love. Let's just say that the two of them are only rarely seen apart after that.
I failed so hard at shading his icicles and armor, but I think the shading of the tusks and spikes offers some compensation. Coloring was a bit challenging because I wanted to tie his color scheme to Beryleon because he has two different colors, red and blue. Beryleon's elemental parts are blue, so I figured Masthemoth's should also be blue, though more whitish blue like ice and snow. I initially wanted him to be blue and white but that didn't look good, so I went first for blue and brown before remembering that Beryleon's color scheme had a nice contrast between the red and the blue. Thinking fast, I was able to apply the hue/saturation tool and made Masthemoth's fur a neat shade of burgundy to match.
The name "Masthemoth" does sound cool on him, despite being whipped up on a whim. It's a portmonteau of "Mastodon" and "Behemoth" that IMHO rolls pretty damn smoothly off the tongue.