If you're like many 40k players, you may have skipped over the section on the Psychic Phase in the 7th edition rulebook on the way to the Shooting or Assault Phase. Unfortunately, the Psychic Phase is now one of the most important parts of Warhammer 40,000. Armies that don't have some sort of psychic capability are at a severe disadvantage against heavily psychic armies. But even if you play Tau or Necrons, or have a burning hatred of warp-users, this article will help you both counter enemy psykers and make the most of your own. If you already know your psykers and psychic tables, skip ahead to the On the Offense and the One the Defense sections.
Overview of Psykers
If, as the introduction suggested, you haven't even bothered to look at the psychic phase, take a moment to read back over it. I can wait.
Finished? Good. Now for some bad news. The Psychic Phase is barely workable RAW, so prepare to go into the mystical land of RAI just to make this part of the game work. Here is a good summation of the rules conundrums about the Psychic Phase: http://www.dakkadakka.com/dakkaforum/posts/list/658118.page There is also a question about how Independent Characters in a non-psychic unit generate their powers, i.e. does the psyker character retain the ability to cast psychic powers when joined to a unit. Check the YMDC section for discussions on just how controversial some of these questions can get.
The consensus is that, because there is no explicit prohibition against doing so, psykers in a unit may manifest powers and psykers may manifest as many powers as they know.
With that out of the way, let's go over the most important aspects of psykers: Mastery Levels, Psychic Disciplines, and Warp Charge Dice
These determine how many powers a psyker knows natively. Because of Psychic Focus and Force, even a Mastery Level 1 psyker knows at least two powers which effectively doubles their effectiveness. In addition, the more Mastery Levels a psyker has, the more Warp Charges it generates in the Psychic Phase. As a general rule, more Mastery Levels are better, and extra Mastery Levels are one of the best upgrades you can give to any psyker that can purchase them. Who doesn't want to have more powers and more dice at their disposal?
These are the tables from which a psyker randomly generates their powers. Not all disciplines are created equal, and many codexes have their own discipline specific to that faction. This guide will serve as a basic primer to the disciplines found in the core rulebook.
Focuses on buffing psyker and friendly units, and weakening enemies. Psykers can become monsters on the tabletop with powers like Iron Arm and Warp Speed. Endurance is a great blessing, and Enfeeble a terrific malediction. Life Leech and the Primaris, Smite, are solid witchfires. Only Haemorrage stands out as a power to avoid. You can rarely go wrong with this discipline.
Focuses on making friendly units more powerful. Special attention should be giving to the Primaris, Prescience. It is one of the best powers in the game, and well worth taking for the benefit of re-rolling to hit in shooting and assault. Foreboding and Perfect Timing allow the psyker's unit to become much more dangerous on the tabletop. Precognition makes the psyker the king of re-rolls, while Scrier's Gaze operates on a more strategic level. Forewarning is a powerful blessing, and Misfortune is an excellent malediction. Overall, it's one of the best psychic tables in the game. You should be rolling on this table if you can, or don't have access to some sort of faction-specific discipline.
Only Grey Knights can manifest from this discipline without suffering Perils of the Warp on any double. Has a good mix of offensive and defensive spells, with a special focus on screwing over Daemons. The Primaris, Banishment, is a great malediction when facing any kind of Daemon, especially one that has been buffed with the Grimoire of True Names. Gate of Infinity is a great blessing, and key to builds like the feared Centstar. Hammerhand and Sanctuary are very powerful blessings, with the latter able to ruin a Chaos Daemon player's day. Purge Soul and Cleansing Flame are great witchfires. Vortex of Doom is too costly to be used most of the time. This table is why Grey Knights are so powerful.
Only Daemons can manifest from this discipline without suffering Perils of the Warp on any double. Focuses on summoning Daemons, one of the most powerful (some would say OP or broken) elements in 7th edition. Note that all summoning powers except Sacrifice are Warp Charge 3, so (as covered later) you will need a lot of dice to get these powers off successfully. The Primaris, Summoning, summons a small unit of basic Daemons. Sacrifice summons a Herald at the cost of an unsaveable wound on the psyker, Incursion summons more elite Deamons, and Possession summons a Greater Daemon at the cost of the psyker being removed as a casualty. Cursed Earth is a great blessing for friendly Daemons. Dark Flame is an okay witchfire, but Infernal Gaze is best avoided. This is the favored discipline of Chaos Daemon players, and with good reason.
Focuses on witchfires that are fire-based. The Primaris, Flame Breath, is basically a Heavy Flamer with Soul Blaze i.e. it's okay. Fiery Form is a solid blessing, especially if you are focusing on Pyromancy. Fire Shield is a great blessing for a friendly unit. Spontaneous Combustion, Sunburst, and Inferno are all decent witchfires against infantry for their ability to ignore cover. Molten Beam is a meltagun; you are better off simply taking a meltagun. A decent discipline, but most psykers have access to better.
The worst discipline. The Primaris, Assail, is a mediocre witchfire. Crush is terribly unreliable for a witchfire, and Shockwave is underpowered. Objuration Mechanicum is a solid malediction. Levitation is a poor man's Wings of Sanguinius, while Telekine Dome is too expensive for a 5++ save. Psychic Maelstrom is too costly for what is does, and just as likely to kill your own psyker. A couple decent powers, mired in a bunch of useless ones. Avoid at all costs.
Focuses on messing with enemy and friendly Leadership. Psychic Shriek is an excellent Primaris power and a useful insurance policy if you don't roll what you want on the table. Special note should be paid to Invisibility, the most broken psychic power in the game. Dominate is a great Malediction and allows you to play some literal mind games with your opponent. Mental Fortitude is an okay and situational blessing. Terrify is a solid Malediction against units that have low Leadership and lack ATSKNF. Shrouding is a solid blessing for the psyker and friendly models. Hallucination is mediocre as far as maledictions go. A solid table overall, as you can always swap for Psychic Shriek.
Overall, Divination is clearly the best discipline, followed by Biomancy and Telepathy. Daemonology is best left to the factions and models that can work around the penalties and costs. Pyromancy is more situational, and Telekinesis is best left alone. Note that if your faction has it's own specific discipline, such as the Eldar Runes of Fate and Runes of Battle or the Dark Angels' Interromancy, it is often worth rolling on those tables, as they are usually designed to be more beneficial to that faction than the generic tables (or, if you play Tyranids, you are forced to roll on their table of powers).
Warp Charge Dice
Having fancy powers doesn't mean anything if you can't cast them properly! Casting psychic powers is a balancing act between the chances of success and the chances of suffering Perils of the Warp. As a general rule, you want to double the Warp Charge cost of a power to get the number of Warp Charge Dice you want to spent to cast the power with any chance of success; add an additional dice if you really need the power to go off.
For example, spending 2 dice on a WC 1 power succeeds 75% of the time with only about a 3% chance of perils. 3 dice on a WC 1 power succeeds 87.5% of the time with only around a 7% chance of perils.
Note that the more dice you spend on casting, the greater chance you have of getting Perils of the Warp. Never spend more than 7 or 8 dice on a single power, as the chance of Perils is around 33% for 7 and 39% for 8, and jumps significantly after that. Spending 10 dice guarantees perils (from a statistical perspective).
It wouldn't be Warhammer 40k without an element of randomness, and this comes in the form of the roll for the number of additional Warp Charge dice both players get for that Psychic Phase. As with anything, there are winners and losers when it comes to this roll. Rolling low benefits the player with more Warp Charges natively, as it prevents the opposing player from effectively Denying the Witch. Rolling high benefits the player with fewer Warp Charges natively, as it allows them Deny the Witch more effectively and cast their powers more reliably.
On the Offense
Now that we have an overview of what powers psykers can access and how to cast them, it's time to go over how best to use psykers on the tabletop. In general, psykers can be divided into two classes: Aggressive Casters and Support Casters.
Aggressive Casters tend to deploy and move aggressively on the table, either supporting or as part of a powerful single unit with their psychic abilities. Maledictions and witchfires are the kind of powers these psykers use more effectively, along with blessings that target the psyker. As such, Biomancy and Telepathy are good disciplines for these psykers to use. Good examples of Aggressive Casters include a Librarian on a bike or in a drop pod with a command squad, Mephiston, and the Swarmlord.
Support Casters tend to hang back in the deployment zone or midfield and support friendly units. Blessings, especially those that target friendly units, are their stock-in-trade, with the occasional malediction or witchfire to handle enemy units that come too close. Divination is the best discipline for these psykers to use. Good examples of Support Casters are a Librarian supporting a unit of Devastators, a Farseer in a Warlock Conclave, and a Primaris Psyker blessing a Leman Russ squadron.
When casting offensively, don't immediately go for the power you really want/need to get off this turn. Instead, bait your opponent by casting a lesser power first. A good example is casting a WC 1 power, followed by a more important WC 2 power. If your opponent hasn't caught on to what you are doing, they will either not attempt to deny (letting you get off a free power), deny with only part of their dice pool (reducing the chances of them successfully denying), or rolling enough dice to deny your power, exhausting your opponent's dice pool and letting you get off the power you really need with no opposition. But if you only have a limited number of dice to work with when casting at all, it's best to put as many dice as you can into the power you need most.
Psykers in any army act as a force multiplier, in that they make normal units even better and more reliable on the tabletop. In any army, the job of the psyker is to support the army as a whole.
On the Defense
Let's say you don't like to use psykers for whatever reason, or play a faction that doesn't have access to them. Unfortunately, there are plenty more armies that can, and they can dominate if left unchecked in the psychic phase. Eldar, Tyranids, Grey Knights, and Chaos Daemons are the most psychic armies in the game. Fortunately, there are ways to deal with even these armies if you know how to defend against psykers and psychic powers properly.
In general, the best defense against psykers is to have a psyker of your own. Not only do they give you extra dice to work with, but also double your chances of denying a power focused on their unit. Psychic Hoods can greatly expand your psyker's ability to deny powers targeted against other friendly units. If you have a psyker with a greater number of Mastery Levels than the opposing psyker, you deny powers just as well as they cast powers (as long as they are not in a Council-type formation)! Any access to Adamantium Will also helps protect units, as it doubles their protection from maledictions and witchfires. Black Templars and Sister of Battle have army-wide Adamantium Will, making them great at stopping offensive powers. Sadly, Shadow in the Warp doesn't do much for Tyranids in terms of pure psychic defense.
Denying the Witch
But what happens if you play Tau or Necrons, who can't take any psykers? And what's the best way to Deny the Witch anyway? There are two basic steps to effectively denying a psychic power.
Step One: Identify the most powerful spell your opponent is likely to cast. What powers a psyker knows is public knowledge, so your opponent can't hide it from you. Special attention should be paid to Invisibility and any kind of Summoning ability, as these are the most powerful abilities and are also extremely likely to be cast.
Step Two: Throw all your available dice into denying this power. This point cannot be stressed enough. If you read the On the Offense section, you should know both the standard tactic people use to bait deny dice and why splitting dice between deny attempts is a bad idea. Unless you are denying on a 4+, you need all the dice you have to get enough sixes to be likely enough to deny a power.
Denying the Witch is a game of prioritizing the greatest threat to your army and throwing as many resources as possible into stopping it. Follow these two simple steps, and your ability to stand against a psychic onslaught will be greatly increased.
Hopefully by now, dear reader, you have a better understanding of how players use the psychic phase and how to use it both offensively and defensively. Hopefully, you'll at least remember the major points of advice: more Mastery Levels are better, never take Telekinesis, use the "double plus one" rule for casting powers, and always deny with all your dice! With any luck, facing down a Chaos Daemons or Grey Knights player will no longer seem like an exercise in futility.