If I've learned anything in my life, from living in a cave, to living in a box, to making a living in that box, it's that everyone wants something. Even if they don't know what that is.
Parva Celia, the self-fashioned Alchemic Mimic, who is storied enough amongst rumormongers and black marketeers to have stories as to how she was spawned(ranging from a demon of greed that steals men's souls and/or wallets, to a treasure so valuable that it began to understand it's own value and start walking around), is what most adventurers, scholars, and off-kilter "historians" and "biologists" refer to as a mimic: a creature who resembles an old-timey treasure chest in order to lure the greedy to the doom waiting within, like a lustrous trap spider.
However, this depiction, like many that refer to creatures regarded as mythical and fantastic, is just slightly askew. A mimic is less like a trap spider, and more akin to something like a hermit crab; there is no such thing as a natural evolutionary track that results in a living manmade object. That's silly. Rather, most stories of mimics were either from would-be looters getting drunk, stumbling into a cave or someone else's property, and opening containers that happened to have been abandoned and become a nest for very surprised wild animals. As with the case of a few, and notably miss Celsa here, they stayed in the box long enough to take it with them later.
Parva Celia, however, is a bit of a unique case. She was once, and in many respects still is, a simple slime. However, having found herself residence in an actual cache of treasure long ago, the goop that comprised her slowly seeped into the prized and valuable belongings therein, breaking them down bit by bit and integrating them into her mass.
This was likewise not an unusual case normally, but these items were magic- adventurers who delve in dungeons and fight ancient scaled monstrosities will gladly tell you tales of equipment and armor imbued with many magical properties in a myriad of ways. In this scenario, however, the items were intelligent, sentient- and while that may have meant they understood the concept of pain as they slowly dissolved over several decades, it also meant that the magic of sentience was absorbed and integrated into the slime as well, thus causing it to slowly form odd, new feelings. Thoughts. Emotions. Personality. Intelligence in general. But what does one do with this newfound knowledge, something entirely alien in their own existence, with a whole new world unfolded before them?
Commerce, mostly.
The goodly mimic, seeing as incredibly valuable artifacts gave her the life she has now, quickly grasped the concept of value, and latched onto it, equating value to longevity- especially considering the idea that absorbing other magical artifacts could have more beneficial effects on her, or at least further extend her already nebulous lifespan. Sure, she could have become some sort of great scholar, changed the world, slowly... but there's really no money in that, and for her, money certainly talks. After all, even great scholars need a research budget, right?
So, she got into the market. From very early on, she styled herself as the quintessential "traveling salesman". If she came across belongings from ruins she found she had no use for, she was sure she could either find someone who wanted them, or convince them that they did- and she often had little to no short supply of merchandise, given how many adventurers would open her chest up and think her a monster, attacking her on sight. She simply had to defend herself! Lamentable, really. Tasty, too! But still lamentable.
Of course, she is not so unwise as to not have her own skills to ply. Treasure either runs out, or gets eaten eventually- and then what is there to sell? Luckily, the mimic is an accomplished alchemist as well as merchant. As it turns out, having an entirely amorphous body lends itself well to mixing chemicals, salves, reagents, and magic in general, and she can often contain or process ingredients or entire potions inside her body entirely until necessary to use or until bottled to sell.