This mod modifies one novigrad merchant's shop, so he sells rare items, which:
- may be missed by player and never aquired later
- are hard to aquire because many quests must be completed first
- are unobtainable due to mutually exclusive choices
- are aquired randomly and are hard to find intentionally
- do not exist in the world of original game
- are quest items which are later removed from player's inventory by quest scripts

Rare items specifically:
- All witcher gear items, diagrams and maps
- All relic swords and armor items
- All weapon and armor item crafting schematics
- All roach trophies
- All Gaunter O'Dimm's rewards
- All armor dyes and their crafting diagrams
- All decoction, potion, bomb and sword oil recipes
- All red, green, blue and monster mutagens
- Potions: Wolven hour, Drowner pheromones, Bear pheromones, Nekker pheromones.
- Tutorial bomb and snowball
- Herbs: Winter cherry, Nazairi basil, Blue lotus flower.
- Starting gear from: Vanilla, Hearts of Stone, Blood and Wine.
- Unique items from Knight Tournament in BaW
- Some character decorations
- Other
    - Yennefer's pants
    - Prisoner shirt and pants
    - Bath towel
    - Wooden sword and wooden plank
    - Hornwall Horn
    - Mutagenerator
    - Magic Acorn
    - Golden Egg
    - Cake (is a lie)
- New items from Complete Edition (v4.00) (modRareItemsMerchant_v1.6+)
    - White Tiger of The West armor set and Swords of the Nine-Tailed Vixen
    - Dol Blathanna armor set, steel Sword of a Thousand Flowers, silver White Widow of the Valley of Flowers
    - Forgotten Wolven (Netflix) gear and diagrams
    - Roach gwent card
If you need Gwent cards, use The Gwent Card Dealer mod. This and Gwent mod are mutually exclusive, because they modify the same files.
You can teleport to this merchant using console command: tptopos(797.56, 1962.95, 9.85)

Warning 1: aforementioned merchant is available between 06:00 and 18:00.
Warning 2: make sure other mods do not override changes made by this mod.
Renaming "modRareItemsMerchant" folder to something like "mod0500_RareItemsMerchant", so it is first alphabetically, might work.
Warning 3: buying some witcher gear diagrams makes some witcher-gear-treasure-hunt-quests unfinishable.

How to install:
Extract "modRareItemsMerchant" folder from archive, move it into ".../The Witcher 3/mods/" folder. Video.

Modded files:
DATA\gameplay\items\def_loot_shops.xml (<loot name="_store__LW_Novigrad_General_store")
DATA\gameplay\items_plus\def_loot_shops.xml (the same but for New Game Plus)