Ok, so not editing this given the comments on the bottom, I would rather leave the mistake here as an example of how wrong we gamers can get it, and the comments will help people who end up thinking the same thing as me!
Any answers to my question in the comments will definately be appreciate though as it does change how I would deal with Grey Knights and use them (this was much more of a theorycrafting than actual practice at least... I would have felt bad for gubbing someone because of this).
Ok so a bit of editting, mainly with
So the Culexus, havent seen many articles on this Assassin, and had a couple of ideas & revelations about it recently, so I figured I would spend a bit of time enlightening people to my thoughts.
The Assassin comes with their standard rules, Lightning Reflexes for an Invulnerable save, Synth Skin for a very basic FNP, Hit & Run.
This particular assassin has some other nifty options, the Psykout grenade for dealing with Daemons & Pskyers, and a Psycollum for BS 10 when shooting at a Psyker or a unit containing one.
The Weapon is where all the fun is at though. Being S5 & AP1 means its not too bad from the off, Assault helps if the Assassin needs to get up close and personnal to finish the job, but the best part is where it gets an additional shot for each Psyker within 12". Being in an army of Greyknights that are all Psykers this brings some very interesting options up.
I am going to look at a couple of ways to ensure this, and to hopefully help you catch your enemy with their power armour off.
When you are playing an army that Deepstrikes then this baby becomes just plain awesome. You can set them up in a decent place in your battle lines, and then watch him unleash anything from 7-
So a couple of different thoughts on how to get the most from your Culexus, hopefully you will find it useful.
Also in this Grey Knight armies abound age you might found a Culexus is an awesome choice, because the second you face another Grey Knight army you should be more than capable of wiping out an enemy a turn.