First things first, what a piranha is to some degree dictates what it does. It sits in a precarious position with 11/10/10 armor with two hull points and an open top. That fragility is partially negated by being a fast skimmer, which gain a 4+ cover save when moving flat out and can move quite a distance when doing so. Piranha are further aided by their ability to take a disruption pod for each vehicle, though they must all purchase or none purchase. The increase in durability the disruption pod can bring has only increased with its rework in FAQ 1.1 and I cannot see a reason to not take such an inexpensive upgrade that works such wonders to mitigate the weaknesses of the piranha's armor.
The piranha's ability to manufacture a 2+ cover save can mitigate it's lack of durability but, like the decision to take any unit, the choice to take a piranha must be based on what can it contribute to the whole of your army. These guys lost my favorite uses from fifth edition: movement blocking and last turn contesting. I do exaggerate when I say that piranhas cannot block movement or create threat zones, but their ability to do so has decreased. When piranhas blocked infantry in fifth edition, they were hit on sixes in close combat, now they are hit on threes. Without the ability to take a save from these hits, piranhas cannot block any marine infantry or anything with strength five or greater without significant risk.
While their ability to contest points is now absent in five BRB missions, they have gained the ability to hold objectives in The Scouring, though this is at the expense of being worth a victory point. I view this as an upgrade because piranhas were very fortunate to be alive at the end of a game of fifth edition to contest and they can now be a very mobile scoring choice, which Tau lack, in one fifth of objective-based missions.
|Pictured: Practical solutions|
I recommend taking the fusion blaster if you have even an inkling of facing land raiders. These behemoths got a stealth nerf that allows piranhas to bring them down and possibly escape. This is because being shot out of a vehicle bars a unit from assaulting during its next turn. I cannot stress the utility of forcing a unit of terminators to not kill something for an extra turn enough. But that is the Mont'ka(Killing Blow) of the piranha and now they can also embrace the Kauyon (Patient Hunter).
Consider the ability of a missile launcher to damage a vehicle if firing at an armor ten facing. Now consider the mobility and durability of a piranha moving flat out on the edge of the board. If the piranha brings seeker missiles, which I normally abhor, it can maneuver to bring the missiles to a beneficial facing and loose them with markerlight support. Yes, this requires both a surviving markerlight source and the additional investment for the seekers, but I believe they can be worth their points as they do not require the piranha to have line of sight to its target. The target may get a cover save, but the changes to cover have reduced the save's effectiveness.
The durability offered by the disruption pod also makes non-fusion piranhas more worthwhile as they can survive to maneuver into the rear rear arc of vehicles and loose five strength five shots into what is usually armor value ten. It requires some luck and possibly favorable terrain, but it can present your opponent with the choice between turning to shoot the piranha and advancing toward the bulk of your army. Make your opponents choose, put them on the defensive.
Well, that escalated quickly and I think we have discovered some more options that either did not exist in fifth edition or were impractical. I think the piranha is going to stick around until the new codex drops, but how they will be used may have changed drastically. No longer limited to a blunt instrument of overpriced destruction and disruption, the piranha now more accurately reflects the variety of methods the Tau Empire utilized in its wars to bring hope to the galaxy.
I'm Underground Heretic and I get to live with that everyday