Blocking with Piranhas
Blocking is a simple concept: enemy units can't come within 1" of one of your units unless they are charging. The Piranha is an ideal blocker. It can cover 30" in one turn and ignores intervening terrain/models. This mobility makes it easy to get the Piranha wherever it needs to be to obstruct your opponent's movement. It has a large foot print, which makes it a bigger obstruction. Finally it has AV11 front armour, making it immune to small arms fire from the unit it is obstructing.
WARNING: with all blocking tactics it is imperative that you watch out for unit types that can circumvent intervening models (Jump Pack Infantry, Jet Pack Infantry, Jetbikes, Flying Monstrous Creatures, Skimmers, and Flyers).Example 1:
A piranha school is positioned so that the marines have to spend a turn circumventing them, effectively preventing any forward movement. This leaves the tactical squad with two options. One is to waste a turn moving around the piranhas and shooting the fire warriors without the benefit of rapid fire. This allows the fire warriors to rain rapid fire pulse fire on the marines whilst only having to take half the return fire. The other option is for the tactical marines to shoot and assault the piranhas. The marines have to shoot the piranhas if they want to assault them as per the core rules. AV11 makes their bolter fire useless, leaving their special weapon(s). Assuming the piranhas moved flat out and therefore have a 4+ cover save, the chances are those special weapons will be ineffective. The marines then assault hurling their krak grenades, most likely destroying one if not all of the piranhas (depending on the number of marines). Units can't consolidate after assaulting vehicles so the marines will have moved a total of 1" that turn! If the piranhas do get destroyed they will leave dangerous/difficult terrain further obstructing the marines in their next turn, potentially giving the fire warriors another turn outside the marines rapid fire range.
What does this achieve? The fire warriors get to fire rapid fire, whilst preventing the marines from doing the same, the marines either waste turn either circumventing the piranhas or shooting and assaulting them. In both cases the marines don't do much. A smart Tau general will have already detached the drones, meaning at worst you have a 150+ point unit spending an entire turn taking out a 24pt unit (2 piranhas are 80pts, minus the cost of 4 drones 56pts). Example 2:
A unit of terminators has just deepstruck, landing near some fire warriors. The fire warriors moved away and rapid fired the assault terminators, killing one, the piranhas have then moved in to block (using their flat out move as they were previously on the other side of the board). On the space marines turn the terminators charge the piranhas destroying them, gaining an inch, and leaving two craters of difficult terrain. The fire warriors move back an inch and rapid fire the terminators again, getting a second shooting phase. On the space marines turn the fire warriors are still 15" away from the terminators, the terminators take a difficult terrain test and move 4", they use their run move to try and get out of the crater and just manage clear it. The fire warriors move away and get a third shooting phase and so on.
In this fashion you can prevent enemy assault units from reaching your line, even delaying them a single turn can give you enough time to pound them into the dust, with practice you can turn a few inches of ground into a mile. The addition of an ethereal invoking storm of fire can make this style of blocking all the more deadly. Example 3:
It is turn 5 and the Tau have gone first. Due to the tau forces being worn thin, a marine squad has somehow survived the Tau shooting phase. The marines are poised to grab the objective, if the game ends on turn 5 the Tau will be unable to stop them, resulting in a marine victory... or will they? Thankfully flat out moves are done in the shooting phase this edition, so you can wait to see how things go before deciding to block with your piranhas. The piranhas move flat out to block the marines, as long as the marine army doesn't have the fire power to down the piranhas they should be able to prevent the marines from getting within 3" of the objective preventing the marines from winning if the game were it to end on turn 5. Again this takes advantage of the fact that units do not get a consolidate move after assaulting vehicles.Example 4:
A land raider crusader full of assault terminators is moving towards the Tau line. The squad of three piranhas flat out and block it, forming a triangle and remaining within 4" coherency. This prevents the landraider from moving forward this turn; if it wants to move it will have to reverse. The contents of the land raider will not be able to perform a normal disembark as all the hatches are blocked; if they perform an emergency disembarkation they will forgo the rest of their turn (emergency disembarking units can't perform any voluntary actions during the rest of their turn). The only way for them to disembark is for the landraider to reverse. The other option is for the land raider to stay stationary and try and shoot the piranhas (though this still stops it from moving, and its contents from disembarking). This does a few things; it stops 300-400 points of your opponent's army getting into position, giving you another turn of shooting it before it gets to your line and also forces him to dedicate a fair portion of his shooting into eliminating 36 points of piranhas (assuming no fusion blaster upgrades, and that the drones have already detached).