which higher being stole mother mosses form/power
the void guardian, god of the second realm, although it lives in the space between the realms (the void) and cannot access its domain.
(stole kinda implies it now wears their form, it doesn't. gods can choose their own form, but any god above them has the authority to change it, for the most part they don't because it's simply a visual thing, but no longer being allowed to have a form effectively makes a god powerless.)
the void guardian's job is to guard the void. like all gods in the upper ranks, it guards its domain from outsiders. mortals are supposed to be restricted to a very limited amount of obtainable knowledge, if they start crossing the line, it's a god's job to hinder or halt their progress. the void guardian can see all within its realm, and it felt that musmoss was giving florans too much knowledge and power, it thought that they (musmoss) was a threat to the hierarchy, so it took their form to stop that.