|Image copyright Games Workshop.|
At 195 points it's the most expensive non-unique HQ choice in the codex. It's hardy enough, with toughness 6, 6 wounds and a 3+ save, but is not as well equiped for combat as other options with 3 attacks and limited anti-infantary weapons. You could end up with some anti-tank options from Warp Blast when generating power of the hive mind, but you'll only get that one in six games so you couldn't rely on it. What you end up paying for is its most interesting ability, "Spawn Termagants".
For those of you that are unfamiliar, "Spawn Termagants" allows you to roll 3D6 a turn and spawn that many Termagants (basic Tyrannid foot soldiers), which is super cool. However, if you roll a double then you spawn that number of Termagants but you cannot use the ability for the rest of the game. With 3D6 it seems quite likely you'll roll a double, but what are your chances? Well using a really simple script you can simulate rolling 3D6 millions of times in a few seconds and count how frequently you get a double. Here's the script:
You could probably do something similar in Excel even, but this sort of thing is pretty simple to do in Python. In the end it spat out that it rolls 556513 times with no doubles and 443487 times with doubles. Obviously that works out as 55.7% of the time you'll get to roll twice. If we expand on this a bit more, we can simulate rolling every turn and seeing how many Termagants are generated on average each game (I ran 1000000 simulations again). Here's the code:
On average 22 Termagants are spawned before a double is rolled, with a standard deviation of 15.773. 22 Termagants at 4 pts a pop works out as 88 pts worth of free models on average per game. Effectively this reduces the cost of a Tervigon to 107 pts, but obviously there will be times when you roll poorly and don't get anywhere near close to that many critters, and conversly you'll occasionally get many more. Even with its more limited combat ability it should be relatively straight forward to make up 107 points in combat.
The final thing to consider is "Synaptic Backlash", which deals 3D6 [str 3, ap -] hits to Termagants units within 12" when the Tervigon dies. The damage of "Synaptic Backlash" can be easily mitigated by not being over-reliant on the Tervigon for synapse and managing your wounds to avoid massive damage to surrounding unit.
Overall, I think it should actually be possible to make back the points cost of a Tervigon just from its support abilities such as synapse, "Spawn Termagants" and "Brood Progenitor" (which gives Termagants within 12" counter-attack), along with potentially more from its power of the hive mind. But I think this'd be a waste in most games, so get it stuck into combat and crush some of those under-evolved lumps of biomass and make back those 107 remaining pts! Before this analysis I was slightly sceptical about the Tervigons cost-effectiveness but I'm a convert and will definitely pick one up. If you're considering using one in your army then you'll need to weigh up how happy you are to add another random element to your strategy.
I'm planning to do a lot more of this type of "Analysis" article in the future, generally focusing on Tyrannids, but if any readers have suggestion for topics for analysis for any army, let me know and I'll see what I can do.