Elixir of Life and Antidote are skippable if you are solo and even in teams. The rest are musts.
@Boerewors
The key powers, I'd say, are Envenom and Weaken. Those are your core debuffs. Alkaloid is a decent ranged single-target heal though the endurance cost is a bit high (but you're stuck with it regardless), and Neurotoxic Breath rounds things out nicely. Antiodte for status protection and Elixir of Life for resurrect (one of the better battle resurrect powers, actually). Paralytic Poison is a ranged hold, which is often useful. Poison Trap is quite different from the Traps version and not nearly as impressive. Noxious Gas requires a henchman anchor and is a decent debuff but in my experience only worth the trouble on really tough targets. Your 1-2 punch of Envenom and Weaken takes apart most things handily without the need for anything else. For AVs/Heros, GMs or PvP, you will want that extra edge though.
In my opinion:
Must Have - Envenom, Weaken
Good - Neurotoxic Breath, Alkaloid, Paralytic Poison, Noxious Gas, Antidote (if you team)
Situational - Elixir of Life
Skip - Poison Trap
I also recommend you read this guide
Iscariot's Guide to the Tri-Form Warshade, version 2.1
I'm sorry that math > your paranoid delusions, but them's the breaks -- Nethergoat
P.E.R.C. Rep for Liberty server
The ones that cannot be detected in a persons blood stream or cells during a toxicology report. 
1. Why Soft Cap is Important : http://dechskaison.blogspot.com/2011...important.html
2. Limits: http://paragonwiki.com/wiki/Limits
3. Attack Mechanics: http://wiki.cohtitan.com/wiki/Attack_Mechanics
4. Rule of Five: http://wiki.cohtitan.com/wiki/Rule_o...e_Law_of_Fives
my thug/poison is lvl 17 atm. Just wondering which poison powers I should get and which ones I must avoid. Thanks