I'm surprised you've only looked at combining the psyker squad with callidus or inquisitor, another crazy thing is using it with the culexus assassin: having a assault 2 +1 for every psyker within 12" animus speculum... say 18+ of your own psykers? =20+ AP 1 shots. Best thing about that is the psykers don't even have to do anything for it... you can use them for some other nasty combo at the same time (IE: divine pronouncement).
Anyone got any thoughts on the best ways to play against the psyker squad? ('hammer of witches' for example)
Well, it may seem like I have over looked the Culexus Assassin, but I didn't. Its just that everyone and their mother around the net is sucking on that teat a little to hard for my tastes.
Lets break down the difference between the Culexeus and the Callidus. We are going to assume you are using the weapon at it's maximum strength? Maximum strength means the Culexus is near 18 psykers for its maximum assault possbility, and the Callidus is wounding against Toughness 2 due to Weaken Resolve and the Neural Shredders LD to T switching ability.
Culexus Animus Speculum
12" S5 AP1 Assault 20
Callidus Neural Shredder
Template S8 AP1 Assault 1
Range - They are both roughly equal here.
Strength - The NS will be hitting against T2 targets (because of Weaken Resolve), so it will be causing Instant Death. Also, it will be wounding most everything in the game on a 2+. Instant Killing multiple wound models on a 2+? Yes please!
AP1 - Same here.
Firing Mode - Here the winner clearly goes to the Culexus for its 20 shots (because of 18 Psykers nearby). Even the NS cannot hope to hit half as many models on a good day.
So what we have here are two weapons roughly equal in killing power and utility. So where then does one outshine the other? In the Assassin itself.
The Culexus Assassin
Lets be honest here... The Culexus is so specialized in a game where Pyskers are not the norm, that you will not be using any, if all, its abilities during the game.
As a matter of fact, to be able to get those 20 shots off, you need two Pysker Battle Squads wholly within 12" for the gun to get its 20 shots. At best, you can have the two pysker squads inside Chimeras driving along side the Assassin within 12".
So for the Assassin to be effective, you need to drive your Psyker Squads up in the enemy's face. Once your opponent knows this trick, good luck getting both Chimeras into your enemy's line past the first turn without getting blown to bits by everything he has.
Should I even mention that your Psyker Squads will be LD 7 during this? Heaven forbid they get blown out of their Chimeras. They might get pinned easier than normal. Plus, trying to pass their Psyker Tests has just dropped from "just about always" to "Flip a coin".
The Callidus Assassin
The Callidus. first off, has 'A Word In Your Ear'. So awesome this power is. Really.
But the strength with this assassin the the safety of your Psykers AND the assassin due to Polymorhpine. With this ability, you can target ANY unit you want to kill on the board.
Weaken Resolve at 36" + The perfect landing from orbit the Assassin does means you WILL be able to kill a powerful unit without your opponent being able to do anything about it. Unless he has Mystics of course :)
This means you can hide and keep safe your Psykers, and only use them when you need them.
This is FAR better than driving two Chimeras next to a lone assassin the entire game.
Then the assassin has the C'tan Sword, a free shitty Poison attack, and Jump back. All very useful. Well, except the Poison attack lol.
How To Fight Psyker Battle Squads
This really isn't all that difficult, and how you do it will vary on the mission, objectives and individual game situations, but, just shoot them up or assault the crap out of them.
If your opponent is using the PBS + Callidus, well, kill that Chimera fast, otherwise kiss your 10 Biker Nobs, Seer Council, Plague Marines, etc good bye.
If your opponent is running a PBS+ Callidus and/or Divine Pronouncement combo(s) you need to kill those Psykers ASAP before anything else! Otherwise you are not going to enjoy your game at all.
So there you have my opinions on both Assassins and their uses with the Psyker Battle Squad. Even against Psykers, I would rather just drop in the Callidus and auto kill the unit in one fell swoop, instead of trying to use the Culexus and dodging fire, all the while trying to get your three units within 12" of a Seer Council :)