The Skeleton Key in Forager is a great artifact, because it allows you to open any chest without having to use a key. This means that once you get your hands on the Skeleton Key, you won't have to create another key at the Forge ever again!
In order to get the Skeleton Key, you will need to complete the quest from the Goblin. In contrast to a lot of the other quests in the game, he will only offer you a single quest, so get it done and be over with it. His quest requires you to get 100 x Bones and give them to him, which should be fairly easy. To get Bones, just attack the tombstones in the Graveyard Biome until it "dies", and then a Skeleton will spawn. Do this until you get 100 Bones to complete the quest, and return to the Goblin to hand them in.
The Goblin can spawn in any random island in the Graveyard Biome, so just keep buying more Graveyard Biome islands to find him.
Once you have the Skeleton Key, it's yours to use forever, and you won't need to worry about keys unless you start a new save file. So get the quest done, because it's a great investment!