I willingly admit that I haven't been able to find the whole series ( I only got up to the tenthbook), so this might be answered later on. That said, HOW DID THE HEROES GET THERE IN THE FIRST PLACE? It's never shown how they were transported to the place, they just imply it's Celia's fault.
In the Anime, we see Celia using a summoning spell to defeat a nigh-unstoppable enemy, which drops the characters and (more importantly) their tank on said enemy.
I've only watched the Anime. In it, there is a super powerful legendary spell that Celia uses, thinking it will banish an evil sorceress which is described as the greatest enemy they had ever faced. However, what the spell ACTUALLY does is transport things/people from our world to their world. So the main cast and tank all fall in, the sorceress mocks Celia because her supposed uber-spell didn't do anything useful and blasts them, so the trio gets pissed and beats the crap out of her. The spell is used again in the anime by someone who didn't know what it did in an attempt to get rid of the main cast. However, it just summons a ton of random crap from our world instead (things like curry boxes and toys).
I know, I know, Rule of Funny. Even so, how is it that getting a spell fragment on her as a dog Shapeshifter Mode Locks Celia that way in the first season, but getting one as an elf Mode Locks her as a werepanda in the second season?
Maybe the fragments prevent the lifting of spells and curses, which would had been very convenient if they had and or used a superpower granting spell on her.