How does upgrading items work?

[DirectOrder]

At the minor forge between levels, you can spend gold to upgrade your gear, but sometimes it will allow me to upgrade to the "+" version, and other times to the "++" version, and other times it doesn't offer the "+" upgrades at all even though the items don't have the "+" upgrades yet. I have no idea why,

Would somebody be so kind as to explain this to me? :) What criteria do you have to meet to be eligible for the first + upgrade, and then what criteria for the second +?

Thanks!

[Fel]

The quality (nothing, +, ++, S or L) adds to the power of the item.
+ gives the equivalent to 2 levels, 4 for ++, 6 for S and 3 for L (but with other benefits like being colourless, costing less to re-roll and such).

[kermat_]

Items have 2 kinds of notations which determine their "strengths": levels and qualities. Levels are the Roman numerals on the item card, e.g. a Blood Sword VII does more damage than a Blood Sword III.
The other one is the quality, which ranges from base to S tier. Example going from weakest to strongest variant of the same sword:
Blood Sword I
Blood Sword I+
Blood Sword I++
Blood Sword I-S
Apart from increased damage, higher levels and qualities benefit from having more affixes on them as well as a chance to get a rarer affix compared to their low-level variant.

The minor forge initially allows you to upgrade an item once, e.g. going from base to +, or going from + to ++. Once you've upgraded that item you can't upgrade it anymore, e.g. you can't upgrade from + to ++ and then to S. You need to unlock "Advanced Forge I" at the collector which allows you to upgrade an item twice. You can still reroll items after upgrading them though.
But there's also the Legendary Forge (the big Blacksmith after a boss fight). Spending cells here lets you get a higher chance to find higher quality items in the biome without having upgraded it. E.g. upgrading the first tier to 100% means you will only come across + tier items from now on. Items lying on the ground, behind golden doors, in chests and in shops will be + tier from now on. The second Blacksmith tier determines the chance for ++ tier items etc. So this means that if you've spent cells here and have found a Blood Sword I+ "in the wild" you can upgrade this sword once to become ++ at the minor forge. And if you've spent cells on the second tier and you come across a ++ item you can spend a wad of cash to upgrade this to become S tier.
By the way, a tip: you can break the Collector's door to carry your cells to the Blacksmith if you want to upgrade your forge instead of being forced to unlock items.

The only type of items that don't adhere to this quality notation are Legendary items. Those are the golden items that you can come across in biomes or if you've managed to kill a boss without taking a hit. Legendary items do have a level but they can not be upgraded as their tier is simply "L".
Legendary items have some other properties:
- they are colorless, meaning their damage will scale with whichever of your stats is the highest (red, purple or green). This is unlike normal items where the background color determines which of the (max 2) stats the damage scales with
- they're forced to receive a special (star) affix and additionally have a 15% chance of receiving a second star affix

[DirectOrder]

Thank you both. That clears things up for me. I appreciate it!

[2A03_Dreams]

hey, thanks -- how do i unlock advanced forge, i checked the wiki but it's not on there (no search results for advanced forge)

https://deadcells.gamepedia.com/The_Blacksmith

[kermat_]

Originally posted by 2A03_Dreams:

hey, thanks -- how do i unlock advanced forge, i checked the wiki but it's not on there (no search results for advanced forge)

https://deadcells.gamepedia.com/The_Blacksmith

Ask the Collector instead ;)
https://deadcells.gamepedia.com/The_Collector