I am going with Curiel
for the first stage.
The "Cu" part is self-explanatory, and I extended it up to curi- of "curious". I mean, with its head like that, it does look like a curious little bugger. It also reminds me of Muriel
from Courage the Cowardly Dog for some reason, so the -el. So yeah, Curiel. Also, it kinda represents the curiosity and cuteness of childhood.
I associate the word gloom with the second stage. It looks, to me alone perhaps, like a gloomy, fat teenager with cool clothes. But hey, silver is a bright color, so Aglume
so as to include "Ag" and mean use the "A" as a negative prefix. The word "glum" is in it too.