It is possible to upgrade any items (including unique items) when going from Act 3 to Act 4. Some of the unique items are really special but they are only useful at low level. After they are upgraded to level 18 the item becomes more useful, providing more damage, more armor and stats boost.

Corbin Day would be in Lady Vengeance if you defeat the Lone Wolves in the sawmill (Act 2). Then you can convince Corbin Day to go to the Lady Vengeance.

In Act 3, before going to the Arena of The One, you have to sell the desired items to upgrade to Corbin Day in Lady Vengeance. After that, you have to fight the battle (Source Titan) in the Arena of The One before going to Arx.

There is another chance to sell the items to Corbin Day, after you defeated the Source Titan in the Arena of The One. It is on the Lady Vengeance, where you can decided to perform romance with the teammate. You can go down one floor to trade with Corbin Day. IIRC, the the item level that Corbin Day owns is now at level 8. The items will be upgraded when you reach Act 4. IIRC some items upgrade in this way may have a different stat compared with items sold to Corbin Day before fighting the Source Titan. For example, The Illuminator, the Necrofire burning would be 1 turn instead of 2 turns.

When you reach Act 4, you can go to the Lady Vengeance (Hall of Echoes). Items sold to Corbin would be upgraded to level 18.

Points to note:

• Item price to buy it back would be high.
  
  
• Not all unique item can be sold. Try to right click an item, if the item does not have "Add to Wares" option, it could not be sold. Examples include: Livewood shield, Spear of Foes, Mordus' Amulet and etc. If you really want to upgrade these items, you can put (reverse of steal) these item into Corbin Day's inventory. These item would not be displayed that they would be on sale. You will need to steal it back afterwards.
  
  
• Working in DOS2 DE only (as of 2018-Oct). For DOS2 Classic, as far as I know Corbin Day does not go to Lady Vengeance after some patch and it is not fixed. I am not sure if this method would work reliability for DOS2 DE in the future.

Please note below method does not always works. I had heard it from the forum. I got it working only once and did not get it work in the next attempt.

As a side-note, there is another way to upgrade items to Level 19. The condition: Having Red Prince on the team. In act 3, sold (unique) items to Shadow Prince. Help Shadow Prince to destroy the mother tree. In act 4, did not kill Sadha in the Portal of Dream. After leaving the Portal of Dream, Shadow Prince appears and he is not satisfied. While Shadow Prince and Red Prince is chatting, you have a chance to steal back the items (upgraded to Level 19) from Shadow Prince by using other characters. I am not sure if Shadow Prince would drop all items sold or unique items after you defeat him.

For stats wise it may be weaker than those Legendary or Divine level items. But if you use Giant Thunder Rune of Power or Giant Venom Rune of Power, it could provide a total of +6 Finesse, +1 Huntsman.

Pros

• The only gloves that have a rune slot (the type of rune slot is body armor, not amulet). So that you can customize the resistance buff needed with different types of runes for different battle.

Cons

• TBD

Pros

• The only ring that have a rune slot (the type of rune slot is same as amulet). So that you can customize the resistance buff needed with different types of runes for different battle.

Cons

• For the rune slot, in DOS2 Classic it can boost about 15% critical chance. In DE all runes are nerfed, it can only add a maximum of 6% critical chance.

For stats wise it may be weaker than those Legendary or Divine level items. But if you use Giant Thunder Rune of Power or Giant Venom Rune of Power, it could provide a total of +6 Finesse, +1 Huntsman. But amulet type rune slot does not increase elemental resistance, it increase dodge, accuracy or critical chance according to the type of rune.

Pros

• The stats and usage are similar to the glove "Second Skin".

Cons

• TBD

For stats wise it may be weaker than those Legendary or Divine level items. But if you use Giant Thunder Rune of Power or Giant Venom Rune of Power, it could provide a total of +6 Finesse, +1 Ranged. But amulet type rune slot does not increase elemental resistance, it increase dodge, accuracy or critical chance according to the type of rune.

Pros

• The stats and usage are similar to the amulet "Lone Wolf Mark".
  
• Provides 15% of Fire Resistance.

Cons

• TBD

Pros

• Immunity to Stunned. Besides the Armor of the Eternal and some gloves that provide immunity to stunned and petrified, it is the only item that could avoid being stunned.
  
• 15% of Air resistance.

Cons

• TBD

Pros

• Most belt would provide stat like dodging or civil abilities (thivery, batering). The stat for this belt is all about combat ability.
  
• 20% Poison resistance.
  
• Grant the skill Deflective Barrier for shield user.

Cons

• None at the moment.

Pros

• Nice blocking chance (10%)
  
• Good stats boost (+3 Int, +5 Cons, +2 Wits).
  
• With the constitution boost of other items, it should be able for Elves to use this item with flesh sacrifice. The shield should still be equipped after using flesh sacrifice. But still need to watch out for Infected status which would decrease constitution.
  
• Grants skill Blinding Radiance
  
• With rune slot. With Giant Masterwork Rune of Power or Mystical Giant Masterwork Rune, this shield provides the physical armor similar to a level 19 shield.
  
• At item level 18, the magical armour is better than the unique shield Lucio (but Lucio provides 5% magical resistance for many elements)
  
• It could be a better shield after reaching Act 4 and before reaching the traders inside Arx. The traders on Lady Vengeance may sell some good shields, depending on RNG.

Cons

• This shield does not grant the skill "Shields Up"
  
• Does not provide any elemental resistance
  
• Need to defeat Dallis in Fort Joy and on Lady Vengeance (the ship fight with Malady) in order to get this item

Pros

• 15% blocking chance
  
• With Giant Masterwork Rune of Power or Mystical Giant Masterwork Rune, this shield provides the physical armor similar to a level 19 shield.
  
• At item level 18, the magical armour is better than the unique shield Lucio (but Lucio provides 5% magical resistance for many elements)
  
• Having a rune slot. So that you can customize the resistance buff needed or stats with different types of runes.
  
• It could be a better shield after reaching Act 4 and before reaching the traders inside Arx. The traders on Lady Vengeance may sell some good shields, depending on RNG.
  
• Easy to get this item in Act 2.

Cons

• Physical and magical armour is upgraded, but the stats remains the same

For stats wise it may be weaker than those Legendary or Divine level items. But if you use Giant Rock Rune of Power, it could provide a total of +6 Strength.

Pros

• The only helmet that have a rune slot (the type of rune slot is body armor, not amulet). So that you can customize the resistance buff needed with different types of runes for different battle.

Cons

• No stats boost like Warfare / 2 handed /1 handed.

This bow is unique, it should be the only bow that can perform piercing damage with basic attack (not counting using skill Marsman's Fang with any bow).


Pros

• After upgrade, the piercing damage is roughly about one third of the original physical damage.
  IMO the total damage should be comparable to a level 19 bow.
  But the piercing damage would ignore the physical armor.
  
• Grants skill Chameleon Cloak
  
• Cause non-undead targets to leave some blood on the ground.
  
• 25% accuracy

Cons

• It does not have rune slot and it does not have any stats boost.
  
• Normal critical chance (5%).
  
• You need Ifan to be in the team or companion. Once got the bow with Zaleskar, you may change companion (companion only, not possible with avatar)

Pros

• 20% of fire resistance. There are more enemies using fire in Act 4. IIRC few amulets (non-unique) provide elemental resistance.
  
• Have a rune slot.

Cons

• Weaker stats boost

Pros

• 20% critical chance
  
• On paper, this hammer can set Knocked Down for two turns (15% success rate) if the target has zero physical armor. On testing, it seems the success rate for Knocked Down is not consecutive for two turns. It should be 15% success rate of Knock Down for first turn. Then another 15% success rate of Knock Down check after the first turn, if the check failed the target would get up.
  
• Grants skill Onslaught
  
• Have rune slot

Cons

• Compared with Voor d'lamas (both items are at level 18). That hammer had 50% cleave damage and 25% critical chance. This hammer don't have cleave damage and have 20% critical chance.

Pros

• If the magical armour of a target is is zero, it would set Chilled status on the target (except target is current having Necrofire status). Another successful hit would frozen the target. The chilling effect does not have a saving throw or check, it works as long as the target magical armor is zero. In this aspect it is better than the 2H axe "Executor Ninyan's Axe".

Cons

• No rune slot
  
• Only have 10% of critical chance.

Pros

• Back in Act 2, this Axe is great for it's critical chance and stats. Sometimes it may frozen target if their magical armour is zero.

Cons

• No rune slot

Pros

• Good stats boost (+3 Str, +3 Int, +3 Memory, +2 Single Handed)
  
• Grants skill Phoenix Dive
  
• With rune slot

Cons

• Does not increase any critical chance

This item is unique, it can set Necrofire on target for two turns (50% success rate and with magical armor check iirc).

On a 18 level fighter with about 8 Pyro, it would deal about 230 Necrofire damage on target for every turn (total two turns). On paper, the Necrofire is two turns. On testing, it seems on the second turn, there is a 50% success rate check, if the check failed the Necrofire on the target would be removed.


Pros

• With the Torturer talent, it should always set target on Necrofire in the first turn on contact.
  
• Provides 10% critical chance for a 1H sword, not bad.

Cons

• No rune slot
  
• Only +1 Pyrokinetic for the stats.

Pros

• Provides 30% of Poison resistance

Cons

• No stats buff

Pros

• Provides 20% Poison resistance with some stats buff

Cons

• Stats buff is weak

Pros

• Provides 20% Air resistance and have stats buff
  
• Have a rune slot

Cons

• TBD