Tales from Titan: A Grey Knights Psychic Phase Primer (Part One)

 Welcome back to the Vault my fellow Grand Masters and Brother Captains. I'm continuing my exploration of the Grey Knights and how to play them in the new 9th edition.  The Grey Knights are unique among my armies in that they have a lot of Psykers available (pretty much every unit can cast a power), and there are Relics and Stratagems which can modify the psychic casting dice rolls. I've found this to be a bit intimidating and confusing, so I thought I'd write a primer to help myself (and hopefully other Grey Knight players) out.

In this post I will be focusing on the likelihood of casting powers, rather than the powers themselves. I will cover the powers in a future post.

It's worth summarising the rules for casting a psychic power:

• After selecting the power to cast (subject to the restrictions specified in the rule book), the Psyker attempts to manifest the Power using a Psychic Test.
• If the Psychic Test is successful the opponent can attempt to nullify the power by taking a Deny the Witch Test if eligible.
• If successfully manifested, then resolve the psychic power's effects.

A Psychic Test is passed if a 2d6 roll equals or exceeds the psychic power's Warp Charge. If the dice roll is double 1 or double 6, then the Psyker suffers from Perils of the Warp (which is a Bad Thing). It should be noted that a double 1 is *not* an automatic failure, unlike a natural 1 for a to hit roll for example. This is important if we start to apply modifiers to the dice roll. 

A Deny the Witch Test is a 2d6 roll which must exceed the result of the opposing Psychic Test. 

As an aside there may be cases when a player may want to re-roll a successfully cast Psychic Test in an attempt to achieve a higher result to make it harder for his opponent to Deny it.

What are the chances of manifesting a power of a given Warp Charge? This is explained in the following table:

So for example manifesting a Warp Charge 6 power will succeed 72.22% of the time. The same table can be used to ascertain the chance of succeeding in Deny the Witch Tests (so if a 7 is required to Deny, then it will succeed 58.33% of the time).

The second row in the table gives the chance of succeeding in a test, if a re-roll is applied after a failed result (via the Command Re-roll Stratagem for example). Note that *both* dice must be re-rolled in this case.

How do we apply modifiers to this table? All Battle-forged Grey Knight Psykers add +1 to Psychic and  and Deny the Witch Tests via the Brotherhood of Psykers rule for example.  This is easy; simply subtract the total modifier from the power's Warp Charge to indicate the value needed on the Psychic Test dice for or from the Deny's target number to show the value the opposing Psyker needs.

Another aside; Grey Knights can stack up to a +3 to manifest a power, thus allowing a Warp Charge 5 spell to be automatically cast!

Grey Knights have access to a set of very powerful Stratagems which further enhance the chance to manifest a key power or deny an opponent's key spell! In summary:

• Psychic Channelling (1CP): Roll three dice and pick the highest two rolls when attempting a Psychic Test.
• The Aegis (2CP): Roll three dice and pick the two highest rolls when attempting a Deny the Witch Test.

Let's see how this affects the chance of success:

The Stratagems make a significant difference to the probabilities!

I'll finish this post up with some notes covering other Stratagems and Relics which can affect Psychic and Deny the Witch Tests.

• Empyric Surge (1CP): Cast after a Psyker casts a power. +1 for Pyskers to manifest powers if they are within 6" of the Psyker who cast the qualifying power.
• Sanctic Shard (Relic): Bearer gains +1 to cast powers and can re-roll the result of Psychic Tests.
• Artisan Nullifier Matrix (Relic): Once per turn the the Bearer (Librarian only) can add or remove 1 from the dice roll of a Psychic test taken by a Grey Knight within 6".

Writing this post has been a useful experience, and has given me some valuable information around what I should expect when casting Psychic Powers using the Sons of Titan; I hope it's of same value to you to.

I'll throw in a final aside; a Charge Test uses the same 2d6 dice roll with a target based on the required distance. These tables will help with the getting the Grey Knights into the Fight; if only there was a roll three dice and take the two highest Stratagem for charges.