Editing Warhammer 40,000/7th Edition Tactics/Psychic 101 (section)

=====More on Summoning=====
* "New" horrors can't roll from Daemonology per Wrath of Magnus/latest FAQs. Whoops.
** "New" is not explained, so it could mean all Horrors ("new" meaning "latest rules"), or only ones that join your army after list creation ("new" as in "conjured").  The FAQ does not clarify.  Either way, summoned horrors can't roll on it.
* Some quick math; you generally want to throw 6-8 dice at the Summoning to make it go off reliably.  A 10-man Horror squad is only Mastery 1 (they're taken in lists because you spend 9 points for a second warp charge, a min squad is crap), so your return on investment is at best 20%.  Even if you successfully cast it 5 times in a turn, you're only able to pull off one more Summoning than you were before, assuming none of your squads get wiped by the thousand-odd points of return fire (you do actually have to pay points for your initial warp charge).  Even if you do, a horror unit minus its warp charge (since that's getting used for recursion) is basically a 10-man unit of Imperial Guard ''without lasguns''.  Making even a hundred more cultist-equivalents for a thousand points of input energy is a bad trade; you have to do something with all that warp charge to actually win the game, like summon Daemonettes (who can actually kill people without using your precious warp charges) or channel a bajillion Flickering Fires out of all those horrors.  Recursion is a fine way to spend your first turn while you advance into range, but make sure you have a plan for how to get work out of it.
* In lower points games, Summoning is an excellent tool for a lot of situations. Summon Bloodletters in front of Spess Mehreens as a Distraction Carnifex (because they will either get shot down or tear MEQs a new asshole), summon Horrors as objective-holders and batteries, summon Daemonettes for messing up infantry, summon Plaguebearers to hold objectives / pluck apart MCs, summon some Flesh Hounds to harrass Heavy Weapon teams or summon a bunch of Flamers close enough to units they can actually kill with their shots. If you use this only to make more army, you might as well leave it. Seekers are much less useful than Daemonettes, and Nurglings are out-performed by Plaguebearers. If you summon those units for a purpose, however, you can easily change the course of the game with it. However, the more points you play with, the less useful this power is. If you summon 100 points worth of unit in a 500 point game, you just increased your army by 20%, which is freaking huge. As the games get bigger, the impact of this spell is lessened, though.
* Also keep in mind that if you manage to pull this power off, it is almost impossible to deny. 3 Warp Charges minimum with no modifier to deny the witch means on average 18(!) dice minimum to negate this, which nobody has, and if they did, they wouldn't blow them all to negate your Summoning.