I've been studying the various rules of the Burning Chariot to try and get a feel for how it would operate in battle and how best to use it and what I've come up with so far is pretty strange which is no less than I'd expect from a Tzeentch unit. Since my chariot has an Exalted Flamer I'm centring this around that type of chariot but I'm sure that when I eventually get around to doing a tactical analysis of a Herald of Tzeentch then that will apply to the chariot as well. Just as a warning this is a long one so if you're not in a reading mood you may want to skip this one.
The vehicle itself is a fast, open topped skimmer-chariot and therefore comes with all the rules that are associated with each vehicle type. Some of these rules create interesting combinations but other rules seem pretty pointless in light of the designer's note which says that the Exalted Flamer cannot disembark. This affects the fact that, as an open-topped vehicle, it is an assault vehicle which allows for embarked units to assault directly after disembarking but as the Flamer can't actually disembark then it happens to be pretty pointless. This pointlessness aside then there are two major points that should be addressed with regards to the chariot being open-topped and only one of them is positive. The upside of the open-topped rule (and this applies to all Daemons chariots as they're all open-topped) is that they effectively have a 360 degree radius of fire because there aren't any specific firing points from the chariot. This means that trying to flank the chariot doesn't guarantee a unit wouldn't get wiped out in the attempt unlike a tank for example. The downside to this rule is that any rolls on the damage table get a +1 modifier that is stackable with any other modifiers so it makes it that much easier to destroy.
On the subject of destruction the term "glass cannon" really gets personified by this vehicle with a front, side and rear armour value of 10 which means that pretty much every hit from a high strength weapon will take off a hull point. While it does have 3 hull points, the fact that each roll on the damage table gets +1 (at least, depending on other modifiers) means that the likelihood of having the vehicle totally destroyed is just that little bit higher. Because of the low armour values it is also at risk from any weapon that is strength 5 or above, though the risk is considerably less than a strength 9 weapon and a strength 10 weapon is pretty much all but guaranteed to blow it up which is obviously not good.
Now that we've got the bad stuff out of the way it's time to move onto the positives of the chariot and then we'll move onto the Flamer itself and we'll start with how it moves. Because it is both Fast and a Skimmer then it can move up to 12" normally and 18" flat out which works very well in combination with both the weapons (or more accurately the Daemonic Gifts) and with another handy little damage dealing tool; the sweeping attack. This allows the Chariot to attack a unit that it has moved over in that movement phase and can roll a D6 per attack that the rider has (in this case 3) and resolves these attacks based on the riders profile with the exception that to hit is 3+ if moving at combat speed and 4+ at cruising speed. One thing to note though is that this only applies to one unit so moving over as many units as possible isn't a great strategy and is likely to get the chariot blown up. A great way to use this is by moving between cover spots that just so happen to take the chariot over one or two units which will not only score a few free hits but if there isn't any other unit in range then the chariot can just attack the softened up unit and either utterly obliterate it or weaken it to the point where it no longer poses a threat which combines well with the Blue Horror Crew upgrade that reduces leadership of any enemy unit within 6" meaning that the enemy unit is more likely to flee.
While I wouldn't recommend using this unit as an assault unit that doesn't mean that it isn't capable of mounting a decent attack. It gains D6 Hammer of Wrath attacks instead of just the base amount which have the Warpflame special rule which has the potential to wreak havoc on the enemy if the dice go the right way (Warpflame in conjunction with D6 Hammer of Wrath attacks can potentially deliver a total of 18 wounds that ignore armour and cover saves but can also give the enemy FnP +1 so it's a risky strategy but as we'll discuss very soon so are each of the weapons of the Flamer). The Flamer will also get 3 attacks at Initiative 4 that also has a high damage dealing potential but carries the same risks owing to Warpflame.
Other benefits of the chariot are that it gives the Flamer an Armour Save of 6+ (bit pointless), and gains the Jink special rule which gives the chariot a decent cover save just for moving. When combining the Jink save with actual cover it helps to keep the chariot out of trouble. Of course it will be the Invulnerable save of the Flamer that is most used as a smart enemy will constantly hammer the chariot with attacks that ignore cover but the combination of cover and Jink will help out a lot against regular infantry and weapons that don't ignore cover.
Now onto the weapons that this is packing; as weapons go this thing really packs a punch as both anti-infantry and anti-armour. Anti-armour comes from the Blue Fire gift that has a range of 18", strength 9, AP 2. It is a heavy weapon that has D3 hits which even with just one shot is still pretty powerful but with 3 hits it can (and will) do a decent amount of damage (don't forget that AP 2 against vehicles gets a +1 modifier on the damage table). The anti-infantry element comes from the Pink Fire gift which is a template weapon with a strength of 5 and AP 3. While the Pink Fire only gets one shot it is a Torrent weapon and so it can be fired over a range of 12". Taking into account that the Flamer can fire from any point on the chariot this effectively means that within a 12" radius around the chariot there isn't a single safe spot for infantry. Of course each of these Gifts carries the devastating Warpflame rule and the reason I say devastating and not potentially is that either of the results can cripple one side or the other (imagine Terminators getting Fnp? They're hard enough to kill as it is).
So what Robin Cruddace, Phil Kelly and the rest of the team have done here is given us something that has a ridiculous amount of damage dealing potential, a really low points cost for what we're getting (100 points for a lot of damage potential) but tempered it with fragility and the possibility of making a bad situation a whole lot worse thanks to Warpflame possibly dishing out FnP like free chocolate at Cadbury World. Again the term glass cannon seems very appropriate here as it is hard hitting and will be quite scary to an opponent but sustained and heavy fire against it will almost certainly destroy it very quickly. A possible way of countering this would be to Deep Strike it off of the back of an Icon or Instrument of Chaos and straight into cover to then lay down some heavy fire. An alternate strategy would be to use it to draw enemy fire for as long as it can to give your other units time to get into position while dealing as much damage as it possibly can before going boom. At 100 points a pop it's not the worst idea in the world to do both; using one to draw fire and allow other deployed units the time to get into position without getting massacred and then bring in another one once the enemy is tied up in close combat. Including all upgrades (Blue Horror Crew and the Flamer taking his 20 points of gifts) we're talking a maximum of 260 points for two of these so running two in any combination of attack and defence is completely viable. Hell for a maximum of 390 points you could have 3 of these and use up your entire Heavy Support allowance for just these although I wouldn't recommend that. I also wouldn't recommend giving the Flamer any of the gifts unless you really feel the need to but that's a judgement call.
To conclude, this unit can fill at least two roles and do them well; it can either function as a distraction unit to cover your less mobile units while dealing some early damage or it can be brought in later as a pretty deadly hit and run vehicle but whichever role you choose to fulfil I give you just one simple warning. Do not under any circumstances leave this vehicle standing still or it will be completely wiped out as though it had never touched the battlefield. Take advantage of the Jink rule, hit hard and try to keep to cover and hopefully this will be a very useful and destructive unit to add to your army.