The following comments are made to show one method of working out how to take a tough unit out.
When it comes down to it, it works like this (trying to cut through all the various comments!).
The Basilisk can hit you anywhere on the board even if you’re behind cover and, as Maureth rightly points out AP3 would knock out the saves of all but invulnerable ones (apart from things like Terminators obviously) and ignoring his comment about toughness which is null – how can you reduce the advantages and what weaknesses are there to be exploited and how?
First we need to work out how to survive….
1) Speed. The Basilisk is basically immobile. Don’t hang around. To fight immobile shooters you either need to very hard indeed (which the Eldar aren’t) or to keep moving. Don’t stay at the same range as you were the turn before otherwise he’ll zero in. Likewise don’t move directly towards or away from it, as this will allow him to easily add/subtract your movement to/from the previous guess. Diagonal moves are best to increase your chances against guess weapons ("You zig, I'll zag").
2) Saving throws. With the Shining Spear example, given earlier, I suggested giving the Exarch an invulnerable save – this is a must in this case. For the non-Exarchs the only save they’re going to get is cover saves – so keep jumping from cover to cover if you can.
3) Scatter. With a small unit it is better to keep them in a tight formation. Large groups should be spread out as much as possible. The reason for this is that with a small group (such as three Shining Spears) any casualties would cause morale checks and, due to scatter, a small tight formation stands the best chance of being missed all together ("a small tight formation stands the best chance of being missed" - Police Squad). Conversely, a large unit is likely to get hit anyway; so spreading them out reduces the number that are under the template. Additionally, don’t clump your units together unless you really have to. There’s nothing more inviting to him than three units that will all fit under the one template.
Addition to the above! Small units should be grouped closely together only if you expect that your opponent will be using the large template against you! When the smaller one is used, it is still better to spread the unit out. The reason for this is, again, scatter - or rather the lack of it. When the small template comes into play all the opponent does is roll to hit and then places the template - a small unit could get seriously damaged this way.
Secondly identify its weaknesses
1) Guess/Scatter. As detailed above – inaccuracy. No matter how good his guessing is (and I’ve been up against some pretty accurate distance estimators myself) the template has a damn good chance of scattering.
2) Minimum Range. He can’t shoot indirectly under 36” range, so close the range down as fast as you can and kill it. Assuming a standard war gaming table size of 6’ by 4’, even assuming that you are fighting corner to corner, this gives a maximum range of 7’ 2.5”. Assuming that you’re using 18” deployment zones, then you can knock off about 2’. Of the rest of the distance, 18” can be covered in the first move leaving you just outside his minimum range – survive one barrage and that’s it. Waveserpents, Falcons and Fire Prisms (all easily able to take him out) would be able to get within the minimum range in one move.
If you are fighting across the table then, once you’ve deployed, you’ll be within his minimum range anyway.
3) Direct Fire. Once within his minimum range he can only hit what he can see – so don’t let him see you. This is difficult if he has multiple Basilisks but, even then, is not necessarily impossible. What Maureth chooses to ignore (possibly because the opponents that he has been up against charge straight at him) is that even if he needed a 1+ to hit with a strength 99 AP1 attack, if he can’t see you, you’re safe. So don’t let him.
Thirdly identify your strengths.
1) Manoeuvrability. All of the Eldar vehicles, when properly equipped, can move/fire/move, so use this to make sure that, if you fail to knock out the Basilisk, you’ll still be in cover when it comes to his turn.
Well, that’s all I have to say regarding killing them with Eldar – I’m not actually sure that an Eldar army would be the best choice, but it’s not bad.
Finally -"knowful" is not a word, it's "Cynical" not "Sinical" and giving the guy an answer that amounts to "don't bother, if you try it on me I'll just blow you away" is not helpful.