Matthias was cooking.
Not literally, but metaphorically. His plans were coming along nicely. What is a merchant without items to sell? It started out humble: acquiring meats, pelts, feathers, and the like for various sentient creatures, who would then trade those items for something else. They were only of slightly better value than what he had hunted for, but with those items he would then trade it for other items, and those items for other items, until finally he had acquired the items to make:
A merchant stall!
Matthias isn't just a pretty face! No, no, he's got the brains, strength, and will to pull something like this off. And with his telekinesis, it was easier to get all the pieces assembled and cut the equipment's production down by days, maybe even weeks.
The stall was a bit bare bones at the moment. It had a cloth that draped over the top and provided shade, one side of it had a harness for when he needed to move it elsewhere, and of course wheels to keep it mobile.
He used the last of his earnings to buy himself a wide satchel, capable of being placed behind his wings/near his rump without discomfort. As well as a smaller one for Roxanne. He would need a helper for all these trips. When the stall had been finished Matthias draped it in leaves, branches, and a little bit of dirt to help it blend in. Then, the two were off, with Matthias helping her use her wings to get to the portal.
It would lead them to crystal caverns - or at least, the entrance. They made their descent, and once inside, began to search for anything of value. While they searched for gemstones and ore, he gave her lessons about gems and their properties, as well as how to distinguish between metals, gems, crystals, or just plain rock. She seemed interested enough, but mostly just wanted to explore.