Grey Knights

I have been thinking of Lady Malys lately when it comes to all the psychic stuff. Am I right to believe she is immune to cleansing flame and heroic ...(can't remember the name)?

If true I will be experimenting with her, I am curious if anyone else tried her against GK yet.

Yea, her and her unit become immune to anything. While nice, GK have plenty of other psychic powers which boost their stats, so its not like it would really be game changing. Sure every army has the ability to take some kind of psyker, but whether or not you'll face one is questionable, not to mention there will be plenty of other units for the psyker to target besides her. I think it really just saves her (and her squad to some degree) from force weapons and the occasional sniper psychic ability.

As for malediction, I've had mixed results. In one game it killed 2 justicars and a librarian (very rare, but DEFINITELY paid for itself) and in other games I've had it completely wiff. I think its only worth taking if you have your build down cold, and have 20 extra points to spare. I would never build a force around it. Even then you'd probably do more damage with a shattershard for 5 points less.

I am finding more and more competative lists of Grey Knights are stepping away from psycannon / purifier spam. Which is nice for dark eldar because that army hurts... Why are they doing that? Because psymandreads are great, they can easily become useless is your metat changes... I used my 4 rhino CSM army at a tourny a few months back... Went up againt the 6rifleman dread army and tabled it... WHY? Because he shot all 4 of my rhinoes off the table turn oe.. Then each dread killed a single model a turn at best... He wasted all those points on dreads... I told him Max 2 Psymandreads and since then he has got top 3 in ardboyz and produces a very very scary GK army...

Purifier spam is expensive and will get rocked in tourny evirnment mainyl cause they are expensive and can have a terrible match up and get tabled ez... I have done it...

I am theming my army Lady Malys for other reason but thing her anti psyker power will be pretty cool vs purifiers and such... Not Game changing though... I am really looking foward to thoseFear the Darkness spam armies that assault dark eldar...

Like most other things, it all depnds on what you face.
Face a palladin/terminator heavy list and GK's are a walk in the park to defeat. However, they have lists that can really give us problems, how about.
3 Psyfleman dreads, 4/5/6 razorbacks with twin-linked HB's with psy ammo, each with 2 psycannons inside. It's got the range and strength to take us down before we get into assault range and has massive short range firepower as well. Probably another match up that could be decided on the roll off for first turn.

Kenny the list you described is atypical of GK round here, its a sh1t to play against , they just push forward and mow any visible vehicle down, purifyers have noting to fear from any DE cc squad , they even go TWICE before Incubi due to the ridiculous halberds.

how about multiple flat out storm ravens that can still shoot and are unstunnable which have a 3+ cover save from shrouding. Short of good luck my current army which contains 20+ darkmatter weps struggles to bring them down, you essentially have one turn to do something significant to it before the contents are on you. with more than one..... good luck with that.

Admittedly this would be less of a problem if DE AT was not so weak.