Battle Psykers in a Guard army

I don't know why more people don't use psykers. They are truly awesome for their potential + point costs, and have won me many, many a game. Both powers are extremely good, have incredible range, and can destroy most non-vehicle units in the game (for under 100 points a unit)! This post goes into some general ideas about the unit, and some incredibly powerful combinations - inquisitors, assassins, demon hunters and more.

The composition - depending on what you are going for, my standard is 5-6 psykers + overseer. Please note, the overseer is not a psyker, and does not contribute to the psyker powers. A chimera allows a great fire base, and you can still use the weaken resolve power if the vehicle is stunned. However, 5-6 in the open isn't bad either, as you can hide them and move a single model to line of sight of the target, without confering a cover save to your opponent (the attack is worked out from the single psyker only). I generally choose 5-6 as it gives you room for losing a few due to perils, or having a few shot up. It isn't a huge number to be a points sink, and generally you don't need more than str 6 or -6 leadership penalty to achieve what you want to do (assuming you are using them properly).

Applications

The bomb. With AP D6, they have a 50/50 of annihilating space marines, and 1/3 of going AP 2. With two squads at strength 6, that is something to be reckonned with! Considering the massive range, these psykers can engage from the first turn for tremendous damage. Use the weapon against mass targets, not large single targets (which is why i prefer the 5-6 rather than the uber str 9). Don't bother targeting vehicles, you have other things that can do this. Though I think the second power is far more devastating, the bomb is an awesome fall back power - so what if your opponent is fearless? Demons dying on 2+ to your str 6 blasts? No problem.

Weaken resolve. Dropping an opponent's leadership for pinning, falling back and rallying. Generally in games my overall strategy is to destroy anything they have that can win the game. Consider two psyker squads dropping two enemy units leadership values. Now combine that with the humble mortar. A single hit wounding space marines on 2's, and suddenly they are pinned unless they beat a leadership 3 roll? 2 Lascannon wounds from that Vendetta of yours suddenly causes a space marine unit to run off the table in the first turn? Or something even more sinister? Weaken resolve truly is game-breaking. Your focus generally should be on annhilating the enemy troop choices. Some ideas to think about --

a) Pinning. Simple - a senior command squad tooled up with 3-4 sniper rifles. Mortar Heavy Weapon platoons. Griffons (reroll barrage you say, at str 6? for 75 points??). Manticores (-1 to their leadership for pinning). You shouldn't be using ratlings, because you have Psykers instead! But most importantly, every time a unit causes a pinning test, they have to immediately take a test - even taking multiple tests in the same turn. All you have to do is wound your opponent, and they are stuck in place.

b) Fall back. In my current list, I field as many high powered guns with long range that I can. Autocannons, lascannons, griffons, manticores, multilasers, heavy bolters, etc etc. Your goal is to kill that magical 25% of the enemy unit to make them break. With lowered leadership, most armies will never rally (keep in mind that if you go first, the power lasts for the entire turn - in your opponents turn he is rallying at -6 to his leadership!!). Making a unit effectively fall back between 2-4d6 removes them from the game, particularly early on. I find Vendetta's in particular very, very effective in this role - not much can stand up to 3 twinlinked lascannons. Kill that 25% and they aren't coming back. Intercepting works as well, particularly later in the game - your sentinels outflank at just the right spot to make your enemy unit keep running (even space marines can't rally if they are within 6 inches of an enemy). Target priority is also very important - early on, you want to kill their troops. Hit them while they are in the deployment zone still! They'll very quickly lose 1-2 units that they were counting on, and begin to play for the draw. Keep in mind that jet packs, bikes and the like fall back 3d6 -- these should be targeted later (though before they reach you).

- Primaris Psyker, shroud
I haven't attempted this yet, but it seems solid in theory. Attach a primaris to a unit you really want to keep alive. Ie, rough riders, huge guard squads, units holding the objective to the death, etc. If you succesfully cast the shroud, all enemy units need to take leadership test to be able to shoot you! With two-three psyker battle squads on the field, you can force your opponent to really think hard about whether he will take the risk or not. Keep in mind this doesn't protect you from vehicles - but if you combine this with blocking line of sight, you should be able to keep a fast flanking unit very safe indeed.

Concluding thoughts --- Psykers are awesome. They can destroy your opponents army, your opponent begins to fear them above all else and tries to take them out as fast as he can - leaving your troops alone to win the game. My units cost only 135 points with Chimera gun platforms, which only enhance their effectiveness (all powers and guns are the same range). Again, weaken resolve is not a psychic shooting power, and thus can be used even if you have moved 12 inches or cannot shoot that turn. There are probably many more things that you can do with these guys as well - and when your opponent says 'but my units are fearless', hit them with the bomb, or drop their leadership anyway and let the callidus do the work.