The Artificer is a powerful caster character in Risk of Rain 2. If you want to unlock him, you will need a little bit of luck on your side! If I had to guess, I would say this has been designed to be a character most people will be able to unlock only after they have played the game for a while.
How To Unlock The Artificer
To get the Artificer character, you will need to spawn the Lunar Portal by finding the weird blue rock that will be hidden in the stage. It is important to do this only after you have 11 Lunar Coins. You will need to a bit lucky on that front, as the coins drop randomly from defeated enemies. There seems to be one of these unusual rocks hidden in every stage, so no need to worry too much if you don’t have the coins, but do find one. There will certainly be more of them during your run.
You will need to give one coin to the rock to spawn the Blue Orb, then find the teleporter and beat the boss. Once the boss has been defeated, do not use the teleporter. Instead, use the blue Lunar Portal that spawns to go for a trip to the Bazaar Between Realms. Give the strange blue vendor there 10 Lunar Coins, and you will unlock the Artificer character, freeing him from whatever trap he appears to have been snared in. Unlocking the Artificer will also get you the Pause Achievement!