Soulbound

As you start to familiarise yourself with the Upgrades and Improvements, Alyx will offer a new Quest.  

 

This Quest is one of, if not the best quest for getting good upgrades for your Starting Weapons, to let you boost a gun you like to help speed up your progress.  
Completing the Quests: “Where the good guns at?” Parts 1 - 6 will reward you with Soulbound Upgrades.  

These types of Soulbound Upgrades/Materials/Resources carry a a small side effect on use due them being handed out by Alyx to help boost your progress-   
Locking the gun to your account so that you cannot trade them, drop them or lend them to others. They are destroyed (with a warning) when dropped!   
    She will Reward you with:

Stat Mutator,Vorpal Shard,Weapons Modkit and aTierifier
 

Stat Mutator

 The Mutator that Alyx gives you has been heavily modified, granting any Weapon its used on to INSTANYLY Gain a Supreme Rating on Stats (+10 to all base stats)  
 However it will apply the Soulbound stat to your  Weapon.