Bound by Flame

For this you will need to inflict poison upon 50 enemies. This doesn't have to be 50 different opponents as long as the victim is inflicted with poison (gradual health loss) it will count. Skills and weapon attachments will increase your "Chance of Poisoning" percentage.

To check your poisoning prowess you can look it up in the menu>Attributes>Negative Effects>Poison enemy - this last section should be at the top of the Negative effects page.
From here you can see your chance of poisoning with Daggers or Crossbow. A zero means there is no chance of inflicting poison with the weapon currently equipped.

Method 1 - Ranger Class - Gift of the Viper - Chance of poisoning with daggers +10% (this will cost you atleast 13 skill points dedicated to the ranger class - 12 to unlock the skill and 1 to get it.)

Method 2 (easier) - Any Class - Craft a weapon attachment with the Poison ability as a bonus. You can Craft Crossbows and Daggers to add a bonus of "Chance of Poisoning" + X%
-If you are not a Ranger class then the crossbow is a better option.

*Easiest Method - acquire the the Crossbow called "DECEPTION" or "ASSASSIN" these crossbows come with a bonus of +75% chance of poisoning - add "Stock of the Serpent's Eye" to the latter for an addition +25% for a 100% chance weapon. Now every shot with the crossbow will inflict poison and you can get this in no time.

How to get Deception - side quest "A Forge for Renko"


How to get Assassin - side quest "Randval the Loner"

This can be done in a few ways.

Some weapons come with the ability to poison by default.

Some weapons can be upgraded to allow for it.

The Ranger skill 'Gift of the Viper' gives all dagger attacks the ability to poison.

My personal preference though is to use the chest armour upgrade 'Chrysalid Eye' which adds +2/s poison and costs 2 leather and 2 refined metal to craft. This upgrade is for the third slot and is available after the Prologue.