Magic artifacts are trinkets that usually do one very specific thing, though weirder and more powerful ones have multiple uses. They have to be charged with coins or juice from a magical being. You can wish up weak ones with silver coins, and stronger ones with gold. They can be lost or destroyed- Not easily, but it happens with the amount of energy magical girls and monsters throw around sometimes. Gods, oni, gremlins, brownies, greater spirits, dwarves, werewolves, monsters, harpies, dragons, miscellaneous, and magical girls or human magi with appropriate talents can make them in an incredibly eclectic collection of methods, too. Some example artifacts: Heal Orb, alarm ward, teleport beacon (one-way), weapons of killing-this-specific-sort-of-thing, semi-infinite water jug, invisibility cloak, various trinkets to blast things with fire or ice or lightning, defensive talismans, magic phones with interdimensional internet, a piece of paper that shows whatever the viewer expects it to, artifacts that shift the local area halfway into the Overworld so all the collateral damage of a big magic fight doesn't kill people or leave odd craters in office buildings and municipal water pipes.