Say you want to play a game of the new Apocalypse but you have a tyranid collection, what do you do? Well before the new release I would have told you to not even bother. Not being able to assault from reserves, D weapons removing whole units of anything at a time, Large no man lands that are death to any infantry to cross them meant little Tyranids could do. Well a few things have changed, some better some worse.
General rules haven't changed that much, except now D weapons don't cause instant death, they instead remove D3/D6 extra wounds. So you are now safe to bring things like trygons and tervigons with out fear of them dying the moment a D blast grazes them.
The rules for the Gargantuan creatures has also changed. While they are still not that much more survivable against missile salvos, though they now have FNP automatically, I've seen no rules that now stop them from benefiting from psychic powers or other effects. This limitation used to keep them from getting buffed, now they can enjoy things like Prescience or endurance.
I find it kind of sad that these gargantuan creatures are really not that much bigger than a Tyrannofex, and most don't even have a 2+ save. The Harridan used to be one of the best that the tyranid could take. It is still a solid choice but is limited by all of the monstrous creature rules for flying. So only 24" movement, can still be shot out of the sky taking a grounding test, etc.
I never have bothered with Formations before, the two of the old ones I liked were the vanguard and the Subterranean. Both of these gave ways to assault out of reserves. With the new edition of Apoc, these have changed and neither allow assaults.
The Vangaurd infestation formation requires broods of genestealrs, atleast one broodlord, and some Lictors. All it does is allow them to be deployed via Lictors (marbo's) placement. This is nice, but still has the same problems genestealers usually have. For the Tax of lictors and broodlord, you can upgrade each stealer brood to ymgarl, and actually have them function well.
A new formation I like is the Living Fortress. This takes two Hive Tyrants, 3 Hive guard and 3 Tyrant guard and creates one unit out of all of them. They automatically have FNP, and can choose to increase their armor save by one but counts as moving through difficult terrain. This is a command formation, so also gives some nice bonuses.
Carnifex crusher brood is just a Carnifex brood that gains a few special rules. The cool one is combining bioplasma together to use a hellstorm flamer template.
Endless Swarm is 30 termagants and 30 hormagaunts. As the game goes on, it becomes more and more likely that the enemy can only snap fire against this formation. This can help keep large blasts off of them, but it is unlikely they will live this long, as they will draw alot of infantry fire. Seeing how everything is generally scoring, I don't see a lot of use for this formation, especially when gaunts don't really do much.
That brings me to Subterranean Swarm. You are required to bring 1+ Trygon prime, and 3+ ravener squads. Once you pay the Ravener tax, this formation opens up the most powerful options tyranids have. Tyranids have no option for D-weapons, even on our most powerful units, so a Thunderhammer terminator squad can easily run a muck through our lines. Not with this formation. Once you have met the minimum requirements, you can then take 0+ Mawlocs and trygons. And by this I mean Mawlocs.
What happens is you deepstrike the Trygon prime first, and he minimizes scatter like a space marine droppod. Once he lands, the rest of the formation deepstrikes and does not scatter within 12" of the Prime. You can use this to place the ravener squad around the enemy and then start hitting them with mawlocs. Units that cant be moved out of the way are removed from the game, and with raveners and trygons blocking their path, this is easily done.
This can hit and remove multiple landraiders, and terminator squads all at once. In the movement phase! Now granted this really isn't much stronger than multiple D weapon blasts, and you're paying around 550 points to initiate it, but it is very powerful and can easily tip the careful balance of Apoc way out of proportion. It will then place multiple monstrous creatures in your opponents face, and this can be done Turn 1!
Another good unit is to throw some Zoanthropes in a pod and drop them on a superheavy. I had recently used a squad in a game, and while they died after their turn, they did some good damage. My initial Salvo on a Fellblade ripped off 7 hullpoints as my S10, AP1 lance shot scored an explosion result each, netting me extra hullpoints. The warmachine was finished off the following turn by sacrificing a Flying hive tyrant assaulting into it.
So tyranid players can easily play in Apoc, and make a stand. Just beware that infantry will generally die very easily, but if you're opponent isn't ready for that many TMCs in their face, it can easily swing the balance too quickly and make for a unfun game. Remember, you don't win at Apocalypse, you have fun!