Disclaimer - I am not an expert on Psychic Power. This is the first army I've really used where psychic powers are a feature.This post is looking for advice more than anything else.
So, with that out of the way (!), here are a few thoughts on the Cult's psychic powers, as it applies to my list.
In my list I typically run a Patriarch and a Magus, both of which are level 2. I usually roll the Patriarch on Biomancy, and the Magus on Broodmind. I typically don’t roll on Telepathy. There are a number of results on the Biomancy discipline that are good for the Patriarch (which I invariably run in a 20 man block of Genestealer), namely Iron Arm, Warp Speed and Endurance. The reason I don’t roll him on Telepathy is that there is really only one power (Invisibility) that is amazing, and one that is good (Shrouded). So, with only 2 dice to roll I think I have a better chance of getting something good on Biomancy than Telepathy. Having said that, 20 Invisible Genestealers would be pretty amazing ……! Maybe the way to go is to roll on Telepathy where my opponent has no ignores cover (making Shrouded good), but Biomancy when they do.
There’s really no compelling reason to roll the Magus on Biomancy (I suppose if you really want endurance and don’t get it with the Patriarch…!), so I usually roll on Broodmind. To recap, the Broodmind powers are
Primarus – Mass Hypnosis One unit within 24” is minus 1 WS, BS, Initiative and Attacks
1. Psychic Stimulus – One friendly unit gains Relentless, Fleet and can Run and then Charge. This is OK, but situational. It would be good on a Neophyte squad with max heavy weapons, but I’m not sure it’s worth taking that squad in the hope you get this power. However, this would be golden if you were facing Coteaz. It would allow you to come in from reserve (assuming you rolled a 6) 12.1” away from Coteaz(so his “I’ve been expecting you” rule doesn’t work), and still have a pretty good chance of getting the charge.
2. Psionic Blast – Range 24” S5 AP3 Assault 1 Blast. Not particularly exciting.
3. Might From Beyond – friendly unit within 24 gets +1 Strength and Rage. IMHO, the best general purpose power.
4. Mental Onslaught – Warp Charge 2, Targets an enemy model within 24”. The targeted model and the GSC psyker roll dice and add their leadership. If it’s a drawn the target suffers a -3 penalty its Initiative. If the GSC psyker is higher, the target takes that many wounds, no cover or armour saves allowed. Again, a bit situational. It kinda depends on their being a crucial model, that doesn’t have a good invulnerable save, has a lowish leadership, and then again it still depends on a dice roll.
5. Mind Control – Warp Charge 2, range 24”. If successful, you control the shooting of one (none vehicle) model in a unit. Because it only effects one model, it depends on their being one very powerful model in the unit to take over. If you can take over a Stormsurge or a Riptide, great, but other than that, again, pretty situational.
6. Summoning – Warp Charge 2 or 3. If 2 you can summon 5 Hybrids, 10 Neophytes or 5 Metamorphs. If you choose 3 warp charges you can summon 10 Hybrids, 20 Neophytes, 10 Metamorphs, 4 Aberrants, or 8 Genestealers. No doubt, this is strong. And being able to upgrade the unit with any upgrades, makes it even stronger. However, it has its drawbacks. First you come in using Cult Ambush, so unless you roll a 6, you have a turn of waiting around doing nothing before you can do anything, and second, it takes a lot of dice to be effective. A summoning list might work, taking a bunch of Magi to provide dice, but it would just make an army that already takes time to play, even more time consuming.
So, strong powers, but not really outstanding. Certainly, none around which you’re whole strategy would turn, and the army certainly works without them. This of course begs the question, is it worth investing in psychic powers? I think the answer is probably “yes”, but not overinvesting. By this I mean, taking a level 2 Patriarch and rolling on Biomancy, it probably a good thing, however a Magus, with the Crouchlling, might not be.
As seems to be the case with most lists, the answer might be “go big or go home” i.e. you either commit to psychic powers and take a bunch of Magi, or you take one Patriarch to go with the Genestealers and call it a day at that. Mind you, for 85pts a Magus with the Crouchling gives you 3 powers, and 2 Warp Charges –pretty good value.