Pathfinders but I've been wanting to talk about them in more depth so here goes. As with everything I write, it's pretty wordy but hopefully I'll cover the vast majority of the things to think about with markerlights. Let's start by looking at how we can get them into our army.
Bringing Light to the Darkness
There's a wide array of choices for getting markerlights into your Tau cadre. The most obvious of which is a unit or two of Pathfinders (11pts per model). As I say I've already covered them in detail here but the key things to note are that they're BS3, static and can only light up a single target per unit. This means multiple units (at least two) are the way to go.
Sharing the Fast Attack slot with the Pathfinders is another unit which can bring markerlights. A Drone Squadron can now be completely composed of marker drones (14pts per model). They have the advantage over Pathfinders in terms of mobility as they're Relentless thanks to their jet packs. This means you can pop out from behind a building, light something up and then hide away again. The price for this mobility is BS2 though which is poor for 14pts. We can do something about that though (more in a bit). Once again there's only one marker target per unit though.
Elsewhere marker drones can be taken by various different units (Crisis suits, Ethereals, Fireblades, Stealths, Fire Warrior Shas'ui, Broadsides, etc) for 12pts per model. The issue here is that they've got to fire at the same target as the unit but the unit itself can't benefit from their hits. This means you might waste marker hits as you kill an enemy unit you've lit up with the rest of your firepower. Of course they're still BS2 as well and their mobility is lost if they're accompanying a unit that doesn't also have jetpacks, such as Fire Warriors. Bear in mind they can be used for Supporting Fire though.
A couple of the HQ choices come with a markerlight too. Darkstrider's is BS5 but must fire at the same target as his unit. This isn't such a big deal as it's only one hit we're talking about but if he's with Fire Warriors (which is probably where he should be) then the hit could be wasted. A Fireblade on the other hand can Split Fire with his BS5 markerlight which may come in handy.
Fire Warrior Shas'ui can take a markerlight and target lock for 15pts. This is BS3 of course but frankly you're probably wasting shots from a pulse rifle and only for a 50:50 chance of hitting with that marker too. Similarly a Stealth Shas'vre can take one but despite being more mobile you're paying 35pts for that markerlight and again wasting shots.
Sniper drone teams are an interesting source of markerlights. The sniper drones aren't particularly brilliant but for 84pts you can get 3 Firesight Marksmen with 3 sniper drones. These all fire at BS5 but again are static markerlights. Still it's a pretty reasonably priced BS5 markerlight and with the reputation of the sniper teams they might be more likely to get ignored plus with the Stealth special rule they're harder to shift than the same number of Pathfinders. The Ethereal can also give the drones an extra shot at 24" which isn't bad. Especially against MCs with their sniper rounds. That'd be 9 shots at BS5, wounding on 4s and potentially rending. Meanwhile you're marking up the target so it can be finished off with a nearby Fire Warrior unit. Intriguing, but I digress...
Finally, as I talked about yesterday, the Sky Ray (or Skylight) is the only ground based unit that can hit flyers with markerlights at full BS. The bomber has a markerlight too. Both units boast the only networked markerlights in the book. The Sky Ray may be BS 4 but doesn't add any mobility to the markers as it needs to stay still to fire both. The bomber is probably going to keep that marker hit for itself if it even hits at BS3.
Commanding the Light
So now we know the huge list of places we can get our markerlights from (I apologise if I've missed any). One more point to cover on this score though. Drone controllers can make a huge difference to marker drones. Attaching a BS5 commander to a unit of 6 marker drones means for a minimum of 177pts you've got 6 BS5 markerlights and 5 hits per turn if you roll odds. That's the same as 10 pathfinders (which cost 110pts) but the drones can keep moving and can hide behind a building, only popping out to light something up before hiding again. Some people have talked about taking larger units or a C&C but with only a single target a lot of those hits are likely to go to waste, 6 drones is plently.
By the way, that 177pts assumes you're only giving the commander a drone controller and nothing else. You could give him some weapons and a target lock though so he isn't just a chaperone for the drone party. A missile pod would be the obvious choice as they're the same range as the lights. However, the cost soon starts spiralling. The unit is more mobile and more survivable than Pathfinders but should it be caught in combat (less likely with Jetpacks) it'll still fold. The other factor to consider is that they don't really add all that much to Supporting Fire. They'll be BS1 like everything else (unlesss the Commander has a counterfire system of course) and that means a single marker hit which, although it will help Fire Warriors isn't as good as Pathfinders a lot of the time.
The commander is so useful in other units (more on him in a different post), that it feels like a bit of a waste of his abilities to stick him in a this unit where he'll also be reduced to T3. I'm going to have to give it a go but the likelihood is that they'll be a priority target and then I'll be left with a lonely commander. Of course a commander could be attached to a pathfinder unit and sit there with his C&C node to help them get marker hits but again, that's a waste I think.
Expending Those Hits
In the old book there were several options for how to use your marker hits (although mostly they were used to boost BS). Now you're limited to either increasing BS by a +1 per hit, ignoring cover for 2 hits and firing seeker missiles.
As I discussed in my Sky Ray post yesterday, "Seeker" isn't much of an option. It can come in handy for vehicles or Broadsides to fire their Seekers at a vehicle or flyer but since they can use one hit to boost their BS and still fire the Seeker it seems a bit pointless unless you really need Ignores Cover.
"Scour" on the other hand is excellent. With a lot of units having Shrouded, Stealth or both there are plenty who can claim a 2+ cover save. Just two marker hits can completely remove this. This is also great for skimmers and bikes who'll lose their Jink save. For your Fire Warriors this is only useful against targets who have 5+ or worse armour but for plasma or fusion weapons it can be huge. Dropping that S8 AP2 ion pie plate with a Riptide and knowing it will kill all the marines it wounds is a nice feeling.
"Pinpoint" is probably the most common boost that markerlights will be used for. The simple reason being that you only need a single hit to take advantage of it. Interestingly there's no maximum to how much you can boost BS like there was in the old codex. Those BS10 Fire Warriors are now pretty awesome for 9pts each. This can also be used for Snap Shots but I'll get to that.
The skill comes in deciding how to expend them. Let's say your Pathfinder team gets a bit lucky and scores 6 hits. You could boost a single 12-man squad of Fire Warriors to BS9. Hopefully you don't need me to tell you that's a waste. Even if they're under influence of an Ethereal and firing 36 shots (makes maths easy), they'd get 30 hits with BS5 and only gain a single hit for every extra point of BS you give them above 5. That means those 6 hits would be better spent making 3 squads BS5 instead. If you need to remove cover then two squads at BS4 with Ignores Cover is better. As you can see there are a lot of different combinations and choosing the right one is key. You don't know how your dice will go though so deciding isn't all that simple.
If there's only one unit that can shoot at a marked target, by all means go nuts and fire at BS10 if you like but realistically you should've probably marked a different target. Target priority is just as important for Tau as it is for any other army in 40K.
Snap Shots and Markerlights
This was something that quite a lot of people were excited about. The prospect of lighting up a target and bypassing the enforced BS1. This isn't all that great in the shooting phase mind you as chances are, whatever you're trying to make easier to hit, your markerlight users will also need 6s to hit. It can be interesting in the assault phase though.
The question is, with your Pathinders is it better to use their markerlights or carbines for Supporting Fire or Overwatch. Obviously it depends on how many other Tau units are around but let's assume you've got a 10-man Pathfinder unit sat next to a 12-man Fire Warrior team. You'd be getting a couple of markerlight hits at best. This means either Ignores Cover or BS3 for your Fire Warriors. Assuming 24 shots that'd be 12 Overwatch hits or just 4 without the markerlights meaning an improvement of 8. The Pathfinders using their carbines would probably get 3 hits. Therefore, it probably is better to use markers with Pathfinders on Overwatch if there's something else around for Supporting Fire.
There's a temptation to get excited and think too much about how many markerlights you can put on a target without actually thinking about what you're going to do with the hits. Sure you can get 14 hits on a target with a commander with 2 marker drones, drone controller and a C&C attached to a 12-strong marker drone squadron but what they hell are you going to do with them? Two 12-man units of BS8 Fire Warriors with Ignores Cover I suppose, but really you're wasting hits. Those units firing two shots each would still only kill 5 marines on average no matter how funny it would be to roll those dice!!
The point is that, whilst it's important to focus your fire on something until it dies, you don't want to waste shots. It's more crucial to be able to mark up several different targets. Despite all of the excitement about marker drones at BS5, I still think Pathfinders are the best choice. Doesn't mean you can't throw in a few other markers here and there though.
Any opponent worth his salt will realise the importance of shifting your pathfinders early. The advantage of markers is that as long as you can see your target it doesn't matter what's in between. Therefore feel free to surround your Pathfinders in a Kroot bubble or deep within terrain. Since their death is pretty inevitable, make the most of them and don't be too tempted to put them on the back line as you'll regret it when their markers aren't in range. Don't be too sad to lose them as hopefully they'll have done their job and in the meantime everything else is still alive.
How you use those markers is pretty much a 50:50 choice. It depends largely on your target. Ultimately, the point is that if you aren't using markerlights in your Tau cadre you're seriously missing out.