The pillow pet is an artifact
See e.g. this Chronicle from Elesta:
Log 1000 04:32 Notes from the dungeon: The heroes plunder the treasure trove and divide the loot. Angel of Death Metal puts 9770 coins, a log for the ark, another log for the ark, a boss monster’s paycheck, a pillow pet and a sacrificial lamp in his pockets. After depositing all their gold into a savings box next to the exit, the heroes ascend to the surface.