A skill with varied materials (that could be gathered from around the realms, through quests or by Rangers/Druids who could then sell it to Rogues) that would allow the PC to, as said in the subject, create a poison of varying strengths depending on the skill of the creator as well as the ingredients involved.
These poisons could then be used for various purposes...
Some could be required for quests, others could be strictly slow acting through foods and the like, while others could be kinds to be applied to weapons before battle.
Paxos
Concoct Poison
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Paxos
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Drakenor
That would be pretty cool, being able to make your own poisons possibly even have special poisons that depend on your class or who you follow, like theives can buy some poison ingredients from a stealth class that only a thief could enter. Some poisons could be like stunning (throwing up some powder in the air and watch your opponent fall to the ground. 
) It could be somewhat like brewing potions (Coded lag, etc. ) Chances to fail depending on your skill level, this would add some excellent rogue roleplay 
) It could be somewhat like brewing potions (Coded lag, etc. ) Chances to fail depending on your skill level, this would add some excellent rogue roleplay -
Selveem
Technically
Technically, the craft 'poisonmaking' is open to everyone. Even fighters can do it. They simply have to spend skill point ranks to increase their proficiency with it. Although, of course, there will always be those who will not/can not use such disgraceful tactics... 
-Ants
-Ants