It occurred to me, when I finally remembered the codex had been released, that I had committed to an army without knowing what it did. I chose to paint my Tyranids as Hive Fleet Jormungandr (well, what I think the artwork looked like, 'Eavy Metal disagree with me, it seems) who were pre-existing but only in so far as they were a name and a completely different colour scheme no mere amateur like me could possibly achieve.
So there was a good chance that GW would write new special rules for them and I had no idea what those rules would be. To be frank, I got lucky because the Jormungandr rules are actually quite cool. As with most sub-factions these days they get an army-wide special rule, a stratagem and a warlord trait. Jormungandr's “thing” it turns out is burrowing. They infiltrate inhabited worlds by landing under cover of meteor shower, burrowing deep down and then undermining the inhabitants' fortifications. They also tend to retain some assets underground so even if defeated they will rise up again.
So how does this work on the tabletop.
To start with the strategem The Enemy Below allows you to spend a command point to set up an infantry unit underground and have it emerge with any Raveners, Mawlocs, Trygons or Trygon Prime. This is an ability usually restricted to the two Trygon variants and that rule only allows you to have Troops choices accompany them. This version allows any infantry unit so that opens it up to thinks like Biovores, Venomthropes, Zoanthropes, Hive Guard and so on.
The army-wide special rule (or Hive Fleet Adaptation) is Tunnel Networks allows any non-flying unit to claim the benefit of cover against shooting unless it advances of charges in your preceding movement phase. Speaking as someone who regularly faces a man who is very, very fond of Front Rank Fire, Back Rank Fire I am very happy with this result.
The Jormungandr warlord trait is Insidious Threat which means the Warlord and Jormungandr units within 3” ignore cover when shooting at enemy units.
At this stage I'm not thinking too deeply about theming the army. I haven't played a game yet and I'm just painting what I could get cheap in bundles or on eBay. I certainly want some Raveners in the initial 50 power list and I'll give some thought to something fruity to spend a command point them out of the ground (Venomthropes, maybe, I like the look of Venomthropes). Aside from that I'm going to wait until I have a couple of games under my belt before I make decisions about where I want the army to go.
Also there will be plentiful Gargoyles because sellers on eBay just can't sell them fast enough or cheap enough to exhaust their supply.