As it turns out, the mystic forge is actually the genie Zommoros. Strange new lifeform? Time for the asura to get investigating.*
The mystic forge serves three purposes:
- Crafting via recipes. Placing specific combinations of items into the forge will yield a guaranteed result. This includes mystic weapons, some of the coolest exotic skins in-game, and legendaries. Unfortunately, Zommoros doesn't list recipes for the forge. They have to be discovered / looked-up on third-party websites (the wiki).
- Upgrades of materials. Common, fine, and rare crafting materials can be promoted into a smaller number of higher tier materials [source].
- Gambling. Placing four items into the mystic forge (of the same quality) will give one higher-level item, with chance to improve its rarity.
I fed 2400 weapons into Zommoros to test out gambling, he gave me the data here.
Placing four items into the mystic forge will yield a higher-level item. How many levels higher?
The forge seems to use average item level for determining upgrades. Four same-level (even identical items) had the same average level upgrade as four items of various levels, but the same average item level.
The pattern is the same regardless of input item rarity or level (usual stats-nerds tests applied).
Both comments on reddit and the GW2 wiki list a roughly 20% chance of upgrading rarity using the mystic forge. Sounds testable.
Take the increased chance of upgrades from blues with a grain of salt. While it is exceptionally unlikely I observed this difference from chance alone, most sources list the 20% upgrade rate as gospel.
Note: the drop-off in level 70+ greens is simply because I didn't record much data there. (Its expensive!)
A few notes on the mystic forge:
- Kamil234 examined mystic forge upgrades with dyes. I haven't tried it out, but he recorded the results here.
- Agronaute threw 1400 rares into the mystic forge and got 71 exotics back (with no precursor) - a 20% quality upgrade rate. More here.
- NonTrivialPursuit forged 50 minis.
- Sub-75 average item level yellows no longer have a chance to yield precursors.
*Now 100% more ethical. Sorry Malomedies.
**Well, I should say, on median. I - very rarely - obtained dramatically higher level items (up to 50 levels higher than the inputs). I'm guessing these are bugs. The items have no vendor value, and are soulbound on acquire. It looks like the item level of the result was just miscoded. Therefore, I excluded these from the analysis. More data required =D.