Ah, the Carnifex; of all of the transitions from 4E to 5E, you suffered the worst. Don't get me wrong, though: whereas before the Carnifex was, hilariously enough, a dedicated shooting platform with shoddy melee ability, now it is at least a reasonable melee threat no matter what else you do with it. The issue is, of course, that it's merely "reasonable," having low WS and I and no Fleet to help get it where it needs to go. Moreover, other critters have overshadowed it at most roles and offer better tank-killing, infantry-hunting, and similar tasks. However, it is also untrue that the Carnifex is completely worthless in the new book, it just fills a much more niche role than you might think from reading the fluff. Let's take a look at some of them.
1. Fexstars
Already talked about some here, but let's review: you want equal numbers of Carnifexes and Primes, so that you can benefit from toughness 6 and cover. Primes get Whip+Sword, 'Fexes get quad Devourers, everyone gets Regen. You can run them as either units of one of each or two of each; the former is tougher (since you can put three wounds on each 'Fex before anything dies, rather than losing one 'Fex due to wound allocation rules), but the latter takes one less HS slot and you can push forward twice as many models with Onslaught. I wouldn't try it at all in battles over 1750, although you might be able to get away with it at 1850, but the general key is "smaller battles means less firepower on the table means more time for Regen to work."
1500 list
Tyranid Prime (LW/BS, Toxin, Regen)
Tyranid Prime (LW/BS, Toxin, Regen)
2 Hive Guard
2 Hive Guard
2 Hive Guard
10 Termagants
Tervigon (Onslaught, Adrenal, Toxin)
9 Genestealers (Toxin)
9 Genestealers (Toxin)
Carnifex (2 Devs, Regen)
Carnifex (2 Devs, Regen)
2. Mass of Wounds
Sometimes, at 2K/2.5K you just have more points available than FOC slots; this is another time Carnifexes can be useful. If you're already fielding tons of MCs, add in a squad of two or three 'Fexes and give your opponent one more thing to worry about. Both naked 'Fexes and Devilfexes can potentially fill this role.
2500 list
Hive Tyrant (2 Devs, OA)
2 Tyrant Guard (Whip)
Hive Tyrant (2 Devs, OA)
2 Tyrant Guard (Whip)
3 Hive Guard
3 Hive Guard
3 Hive Guard
10 Termagants
10 Termagants
10 Termagants
Tervigon (Adrenal, Toxin)
Tervigon (Adrenal, Toxin)
Tervigon (Adrenal, Toxin)
Harpy (HVC)
2 Carnifex
Tyrannofex (Rupture)
Tyrannofex (Rupture)
3. Cheaper T-Fex
Especially in the 1750-2000 range you often find yourself wanting to bring a bunch of guns in your HS slots but unable to really afford Tyrannofexes- which are rather pricey beasts at best. In these situations a Carnifex can work as a budget option, costing 2/3 or so as much as his big brother. Is it much worse at the job? Certainly so, but you don't always have the points to bring in exactly what you want. Devourer/HVC 'Fexes provide a reasonable amount of suppression fire for a reasonable price, and especially Rhinos they actually have marginally better shooting performance than the T-Fex, range aside.
(No list is provided for this because it's hard to draw "general" examples for it; it's by far the most specific of the three uses.)
What they aren't:
1. Deep Striking Threat
Tagline: "You can bring it in with a Mycetic Spore and use Bio-Plasma/Devourers/Scything Talons to do a lot of damage!"
No. First of all, how much are you paying for this? At a MINIMUM, 200pts. Trygons cost 200pts,, and they start with two more WS, Wounds, and Attacks. But you can upgrade the Carnifex into having guns, right? Trygons start with a gun and if you take the Prime, you get the same number of shots as twin Devourers and don't have to trade out all your combat prowess to do so. Oh, and you're a Synapse Creature and have SitW, etc, etc. Bio-Plasma is trash; there is a reason Plasma Cannons are not a popular gun these days. Anything the deep striking Carnifex can do, something else can do better.
2. Tank Chaser
Tagline: "With dual Talons they're a pretty cheap way to kill off tanks, and they can't be ignored!"
First of all, 160pts isn't "cheap" in my book. Three Hive Guard are 150 and will do worlds better at getting rid of tanks; so will a Harpy at 170. (Twice as fast and has an actual gun.) There are plenty of reasons to want a way to kill tanks in non-Elite slots, but Carnifexes aren't it. The opponent can ignore them for 2-3 full turns, which is exactly the opposite of what you want with an aggressive army. And again, Trygons do the same thing for only a limited increase in cost- Fleet and two extra attacks means they are far, far more likely to actually do the job. (Reminder: do not rely on melee to take care of tanks for you, unless you have a way to suppress them first.)
2a. For Killing Land Raiders
Tagline: "Its the most efficient way to kill a Land Raider, hands down."
Sure, as long as the Raider is empty and your opponent fields nothing but Land Raiders. But when you have to start dealing with other units, the Carnifex looks likes a lot worse deal. What's inside that Land Raider? Is it TH/SS Terminators? Because if so, the Trygon has an actual chance of taking them out (it should kill 1-2 of them when charged and has a chance of actually surviving their assault, assuming no other damage) whereas the Carnifex is meat, maybe taking out one of them if you get lucky. Trygons are better able to catch vehicles of all types- including Land Raiders- and are still MCs, and thus have a pretty fair chance of getting a penetrating hit on it even at full speed.
3. Scary in Numbers
Tagline: "They're bad if you just have one or two, but if you take a whole BUNCH the opponent can't deal with them all!"
In a world where armies have infinite points, perhaps this is true; nine Carnifexes is more than most armies can easily deal with. They also clock in at over 1500pts by themselves, never mind actually adding functional units to your army if you don't want to draw every game. Even just 3-4 of them is a huge investment that could be better spent elsewhere buying MCs with more durability and more uses. Target saturation is a good plan, but it's just as important to saturate them with dangerous units that can otherwise perform well.
