Hello. Before I begin I am speaking from an old nids prospective. Once I play new nids i'll add additional information later. However anyone that wants to can add in any additional experiences they would like to add.
Last nid codex I went unit defeated against Tau. However keep in mind this is two games I played where I was nids. Also keep in mind when I play Tau I utterly wreak nids with little effort. Expect to take losses against the Tau is all I can say.
This topic is hard to really talk about due to different Tau builds. You either have tide and broadside spam, riptide spam, heavy Tau troops, Skyray spam, heavy pathfinders or they use marker drone squads, or marker drones in units, and even HQs can vary from O'SHOVA, O'shova and stealth girl, ethereal, swiss knife commander and fire blade.
Depending on how received and how much time I have I can cover more specific strategies. How I will cover a broad outline which should help that nid player defeat Tau players.
To be clear from what I gathered from the new nid dex so far and my experience with the old one I will say nids have an up hill battle for them to overcome.
I wouldn't suggest getting into a shooting competition with Tau. They have all the advantages that you don't have. You might be able to put out more over all shooting, but they can deny cover, shoot further, shoot better, have better shooting weapons, etc. You simply can't match it, don't try to. However you can shoot at key units, or disrupt units that is causing you grief.
#1 combat: combat is your advantage and terrain is you friend. Tau have 3 strengths that keep them out of combat and kill you dead.
A. Cover denial. Lack of cover saves will cause you to loose more units. You really need cover saves. Kill dem marker lights if possible. Ranged shooting is excellent in taking out pathfinders and the such. The Swiss commander and drone combo can only really be taken out with ap 2 shooting or with a lot of fire power causing a lot of wounds. If you think you can kill it shooting go for it. If not just ignore them since they can be a hard target.
B. Tau can wound your stuff on 2s and ignore armour saves on all your stuff from ion guns to even the lowly kroot rifle. Triple tap range can wipe out whole units with ease. For example it is possible for 12 fire warriors to shoot 48 times which is quite capable of taking out 30 gaunts really easily. This is where tervigons actually come in. At best you can run 6 30 man gaunt squads, however it is quite possible for tau to kill all of that in one or two turns. However the tervigons bring to the table more squads. Squad numbers is an advantage against Tau. For example Tau can easily destroy armies with just 10 units and will struggle against armies with 30 units. Unit saturation is the key here over unit volume.
Basically you want your whole army in the Tau face at the same time. Waves really don't work since Tau can easily handle them. Every game I won was due to mix assaults in the third turn with my entire army. Tau will have to choose who they want to combat with. I guarantee you they don't want it to be poison gaunts, I rathera trTrigon assault my squads than poison gaunts, simply due to the squad possibly tying up the trygon, while the gaunts kinda keep coming.
C. Over watch. Which goes back to b. When you think your shot up army has been shot up it is gonna be shot up again. Here having multiple units that can assault comes in nicely. You want your weakest units to assault the shootiest units first. This way your stronger units can assault without being shot up. The Tau player will lose shooting attacks if for say he chooses not to over watch two gaunts not the charge with 20 gaunts sitting right next to them.
Another tactic that have been working rather well was deep striking MCs and outflnaking tervigons. This worked rather well since by turn 2 I had MCs that's in the Tau's face. Plus my army was in triple tap range. If the riptides use interceptor it would not be *** effective as waiting to shoot during the next shooting phase. Plus it's unlikely they can down a deep striking MC anyway through interceptor.
With all that being said the Mawlock may be of use since it can devastate units and if it misses it is still a threat that can tie up broadsides, etc. Personally I am liking a trygon deep striking in and flaming dem marker drones, pathfinders, or ethereal units.
