attached files are of a turtle-trial spawner mob concept i had, feel free to grab it
ars doesnt really have anything related to trial chambers and dungeon loot at the moment
wouldnt something like loonium from botania be fun?
the basic concept of a mob that i thought of is:
feed it source or keys and it will make its own arena with extended mageblocks and spawn a couple mobs
when the mobs are dealt with, it gives trial spawner loot, (and maybe more loot if it wasnt hit in the crossfire)
as a familiar they occasionally grant some mobs resistance III but also makes them drop dungeon loot on death