Next Gen compatible version of my original mod: Here

Description
In Hearts of Stone, you can obtain the Viper Venomous silver sword only by challenging Mr. Mirror and then finding it placed in a rock. You can’t obtain it later if you miss the location where it is or if you decide to let Olgierd die. The only other way is to use the console commands. This mod aims to allow you to get the sword by crafting it if you can’t obtain it anymore or by other means without the need to use the console commands.

There are 3 versions available:

Version A
The schematic is placed in a chest where the schematic for Viper Venomous steel sword is located. Thus, you can find it during the quest Open Sesame! in a chest to the left of Max Borsodi’s House in the vault during the heist.

Version B
If you think that Version A is too OP, then there’s Version B for you. This version will automatically add the schematic into your inventory after finishing the quest Whatsoever a Man Soweth... But it won’t add the schematic if the quest is already completed.

Version C
The schematic is placed in a chest that must be looted during A Dark Legacy. The vanilla reward is very underwhelming given the fact that you have to buy Count Romilly's Figurine for 300 crowns during the auction. Now the reward is more worthwhile. Suggested by Hateshinai.

It's possible to install all versions at the same time. Both the standard and NG+ version of the schematic is functioning.

Fully compatible with Brothers in Arms – TW3 Ultimate Bug Fix Collaboration, Ghost Mode and Witcher 3 – Enhanced Edition.

Installation and Uninstallation
Simply put the mod folder into your Witcher 3 directory/mods. If this is your first mod, then just create a new folder called "mods" and put it in there. Mod Manager will probably work too. To uninstall, simply delete the mod.

Conflicts
Use Script Merger to fix potential conflicts.

Special Thanks
My thanks goes to paulr0013 who gave me suggestions how to approach this mod.