Against Bikers

Hello
Im going to attend Pair Tournament next week and my ally is playing Tau. I want my list to have some sort of defense against white scars bikers who will definitely want to assault him, but cant decide what would be best. t5 3+/4+ cover seems a bit hard to kill in melee. I know easiest way is to shoot them with splinter but I cant count on killing so many bikes before they get into melee.

Has anyone played against SM bikers and had some success?
Thanks

Played 1250 vs White Scars. Something like 2 units of kabalites w/cannon in Raiders w/racks, 2 venoms w/wyches, and a splinterborn venom. They'll likely have a 2+/3++ captain in front; use your speed (especially the venoms) to get side angles on the big squads and take out the rest of the bikes without worrying about that captain. Tabled him Turn 6, on Relic. He had dev centurions as well, with bolter dakka and missile launchers slogging upfield. Those were put down entirely by 36" cannon fire. I made the mistake of underestimating his speed and he got a few charges off on me, but it was all about weight of fire to take down what basically comes out to expensive marines as far as our poison spam cares. Sure you won't get all of them before they get close; that's what the wyches are for.
Speedbumps. Don't charge with the wyches, get him to charge you. Or countercharge with them once the bikes are already in melee.
Best of luck!

Let Tau take Inquisitor allues and use servo skulls to limit Scars deployment.

One of my newer favorite units is 25 khymera with 5 BM. You could bubble wrap his entire army with that pretty much lol. Bring nothing else but venoms and kabalite warriors and 3 man splinter cannon trueborn units. Put a haemy with the khymera squad at the start for a pain token... Maybe? I haven't had too many issues with biker armies. If your tau friend brings Aun Va, I don't think you'd hae too many issues anyway. He gets 3 shots per guy at 15" range and 2 at 30". And that counts towards over watch too. That's a lot of FP. 6x12 man warrior squads with Aun va hiding within 12" of all of them. Throw in some broadsides with pods and smart missile systems, pretty sure he'd have himself covered lol. You would pump out 7 venoms with 2 more trueborn squads with a khymera squad for safe measure. Sounds nasty to me. Although I'm not sure if you could fit all that in your point allotment, whatever that may be. Bring some ravagers and you're good to go.

Having played against a friends white scar list a few times now, I'm surprised how well dark eldar can do. Like people are saying, splinter fire really does whittle them down fast if you focus on a squad at a time. Also I found a agoniser succubuss helps give some effective counter punch when they closed in. I'de give you a warning about using ravagers though, I didn't face much armour but both the lances and dissies I found poor against the bikes.

90% of the battles were about movement though, stay back out of range/ fire, focus squads down ( one MAYBE two bikes, you can get away with assaulting our transports) and then bubble wrap, Bottleneck and counter charge, play dirty like dark eldar should

As doomseer stated I would recommend beasts + baron. Grots will also do well as counter assault since both units are tough and inherently nearly immune to grav weaponry. Other than the excellent ideas already suggested I'll add that from my time playing ravenwing bikes can also be hard countered with smart placement of objectives. Of course allies will effect this strategy but it's good to keep in mind for objectives and also due to their short ranged weaponry.

I would be cautious about bringing assault units. A mate of mine loves the shenanigans that Kosarro Khan brings to the table. They can scout all the way through a 24" zone in no time and then hit and run out of assault fairly reliably. I found my assault units getting marooned and shot at. Although Grotesques laugh at Grav Guns, even they fall to mass t/l bolter fire. A dissie ravager is pretty punchy and giving up ground to redeploy and play savvy is key to the win!

Your mobility is key, the ability to redeploy invaluable.
Hmmm. I'd say split your deployment. The Tau in one area, you in another, force your opponents to either split there forces or choose to go after one of you. If they split there forces, you have the speed to redeploy and team up with the Tau against the half sent after them. Or you have the speed to draw out his forces on a merry chase.
Its likely they know that your fast so chasing you is pointless and they may very well commit there entire force against the Tau. Ignoring you at there own peril, you'd be left to there flanks as they move towards the Tau.
If your intent on keeping the Tau alive deploy a counter attack unit with them like Grots or Incubi, if the Tau line gets hit you can use them to hit right back.

Also, if you want to win, and I am not saying that DE cannot win tournaments, but Desperate Allies means that you can't even deny stuff late game to help each other out. I guess you would have to play hyper aggressive and throw caution to the wind to cripple the opponents you will face. Is there a chance of you having to use a random deployment set-up in any missions? You may HAVE to share space with your buddy. If you roll a 1 to get "one eye open" it can be so utterly infuriating to do nothing for a turn.
I ran Tau with my sons Space Marines in a recent tourney and we kicked arse. I hated our immobility(Line breaker, what's that?) but Tigurius could buff shooting and defense so well it blunted a lot of my opponents advances. We went second all the time and picked apart units surgically to win our way to 2nd. My recommendation, which is too late now probably, would be to find a battle brothers ally, if possible. If your mate has Eldar, great! Stay DE and further our cause!!

In response to above I would have to say there is ALWAYS a weak side.  I always flank on the weak side.  Let your buddy deal with the heavy shooting for a turn allowing you to get in position.  Wherever the heavy hitters are or excessive amount if shots, set up on the opposite side of that. Generally if you am collapse one side, you can move in for the kill.  Make the tau seem big and juicy with obj.s on their deployment and sweep them on the weak flank.  Leave the khymera in a spot to protect them (if you bring them).  If not khymera, leave some close combat units to deal with assaults on your tau friend, run your venoms or whatever young have on the opposite.  Itll not only allow you to focus your shots till your targets are dead but it should also cause your opponents to make more decisions.  The more decisions that need to be made the more room for error.  Our army loves opponents making mistakes.  This usually why I bring a unit that gets in their face quickly, under pressure most opponents make quick impulsive decisions that usually lead to a victory for me.  Pleas let us know how your fight turns out man.  Would love to read it.