Tyranid Tactics: The Tyrannofex
The Tyranid book is filled with all sorts of beasts with specialized roles, and the Tyrannofex is no exception. This hulking beast is one of the most (if not the most) difficult monster to kill in the Tyranid book, sporting a Toughness of 6, with 6 wounds and a 2+ save, making it neigh invulnerable to weapons that seem to be dominating the game lately, such as missile launchers and Psyfleman dreadnoughts. Inside it's armored shell, the Tyrannofex supports a wide array of weaponry, both for anti-infantry and killing tanks. All of the Tyrannofexes weaponry and armor does not come at a low cost however, and each one of these monsters are going to run you from 250 to nearly 300 points when fully equipped.
Before we go on about the main weaponry, lets briefly touch on the Tyrannofexes additional guns. Like other big bugs, it has the option of choosing between the Stinger Salvo or Cluster Spines. The Stinger Salvo offers you a mid ranged S5 AP4 four shot gun, but the preferred option is the Cluster Spines, which is also S5, but instead of four shots, you're getting one large blast.
Aside from the standard Stinger Salvo/Cluster Spines, the Tyrannofex comes standard with a Thorax Swarm, with the choice between Electroshock Grubs, Desiccator Larvae and Shreddershard Beetles. The Electroshock Grubs are pretty standard at S5 AP5 with nothing special going on, but for me and many others, the real choice is between the Desiccator Larvae and the Shreddershard Beetles. The Desiccator Larvae are only S1, so they won't be hurting any vehicles, but they're also Poison 2+, meaning that if you hit 6 space marines, you'll probably wound 5 and kill 1.666, which are pretty good odds for a little flame template. The Shreddershard Beetles on the other hand are S3 but rending, giving you the chance to even kill the odd terminator, though using the same example as the Desiccator Larvae, they come in marginally less effective and would kill 1.555 marines.
Now that we have the little guns out of the way, lets head to the main course, the Tyrannofexes primary weaponry. The Tyrannofex comes standard with an Acid Spray, which is a 12" S6 AP4 flame template attack, kind of like a mini Hellhound. I actually really like this weapon, though it is by far less popular than the Rupture Cannon. If you know you're going to be facing against mid-low AV opponents who lack power armor, then this is a solid choice as the flame template will deny them any cover saves, and it also compliments the secondary weaponry quite nicely.
The second choice for the main gun is the Fleshborrer Hive. This gun has an impressive 20 shots, but unfortunately that's where it ends, as they are simply 20 Fleshborrer shots, meaning an abysmal range and strength. Sadly, I would never take this option, you could get 20 Fleshborrer armed Termagants for less than half the points of the Tyrannofex, or you could get 26 armed with Devourers, which is a staggering 78 shots with longer range! I hate to say it, but this gun has no place in the Tyranid army.
The last choice is vastly the most popular, the Rupture Cannon. This is the longest ranged weapon available to Tyranids, at 48". Using it's impressive Strength of 10 and two shots, this gun is pretty much the ideal (and only) weapon for blowing apart heavily armored vehicles at long range. The only down side to having such an impressive range is that you need to keep it advancing within Synapse Range, otherwise you're going to end up lurking in some cover and shooting something silly.
The Tyrannofex has three biomorphs to choose from, Adrenal Glands, Toxin Sacs and Regeneration. I don't think that this monster is something you really want to be rushing into combat, and spending 10 points to make it better in combat just seems silly. Regeneration however may be a somewhat okay way to protect your investment, but as soon as you do this with a Rupture Cannon, you're almost at 300 points
Use in Game
To quote my favorite 1997 film, Contact, "why build one when you can have two at twice the price?" When you're using Tyrannofexes, one is good, but for only twice the price you can have a second! When you only have one on the field, it will be sucking down every lascannon, multi-melta and anything else that is AP2 which can take down your armored bug, but when you have a pair of them, it's immediately cranking the threat level of your army up to 11.
Towards the end of the game, since your Tyrannofex will probably be advancing with the main army, it isn't always a bad idea to have him charge in to help out with an extra 3 S6 attacks that ignore armor, but be sure that it's a combat that you'll get out of after a single round, otherwise you'll be wasting a turn of firing just to punch a marine or two.
Protecting your Investment
The Tyrannofex is a big point investment for your army, and if your enemy has any tanks at all, you can be sure that they will do everything they can to eliminate your toy. Two of the most dangerous threats to your monster are Dark Eldar Wych squads with Agonizers and Blood Angels Storm Ravens.
The Wych squad will often be deployed from a lightly armored Venom, and it will tie up your Tyrannofex until it is dead. The leader of the Wych squad often comes with an Agonizer, which wounds on 4+ and ignores your armor, meaning that you are pretty much screwed since that bypasses all of your defenses. When you go to strike back, the Wyches are getting their 4+ invul save, pretty much meaning you will do nothing to them in combat. The best way to protect yourself from these menacing enemies is to keep your Tyrannofex protected by a unit that can either counter charge, or can bubblewrap him.
Blood Angels Storm Ravens are another huge threat, as in one turn they can unleash a volley of 4 S8 AP1 missiles, plus a lascannon and a multi-melta if they're close enough, which could effectively vaporize your monster in a single turn. The only protection you can hope for to defend against this kind of alpha-strike is to hide in cover, which may not be easy for a monstrous creature. One important thing to remember is that while you may feel compelled to catalyst your Tyrannofex, the weapons that you have to watch out for the most are going to be AP 1/2, which doesn't allow for a FNP save, so unless you know he's going to be suffering from a withering hail of small arms fire, you're probably better off using catalyst on other creatures.
Well, there we have it, Tyrannofexes can be a valuable asset to your army, but just like anything else in the Tyranid book, it is very specialized and if you have no need for it's specific talents, he wont be offering much. If you're going to try one out, I definitely think you should try two instead, the extra gun and survivability will add a lot to your long-ranged game and hopefully pop some land raiders so you can charge the gooey insides with your Genestealers.