The Tyrannocyte (read, Tyranid version of the Drop Pod) adds SO much to the forces of the Hive Mind, it is almost impossible to capture all the possibilities it opens up and how much more effective it makes Tyranids in the competitive scene.
That said, I think one of the potentially most effective uses of the Tyrannocyte is to drop a Tyrannofex (or three!) in your opponent’s DZ starting turn 2. With the ability to take effective template weapons, it can deal with hordes and even threaten MEQs with its shooting on the turn it comes in on. From there, its 6W, T6, and 2+ save (basically the toughest MC in the game against most armies) means it can absorb some serious return fire (which, by the way, is now not being shot at the rest of your army) and be prepared to charge critical enemy units and Smash them up good and proper.
To illustrate its survivability, let’s take a look at some common weapons shooting at the Tyrannofex:
-BS4 Bolters — With 66% chance to hit, 16% chance to wound, 16% chance to fail an armor save, and 6 wounds to get through, it would take 324 BS4 Bolter shots to kill a Tyrannofex!!
-BS4 Plasma Guns — With 66% chance to hit, 66% chance to wound, and 6 wounds to get through, it would take 13 BS4 Plasma shots to kill a Tyrannofex.
-BS4 Krak Missiles — With 66% chance to hit, 83% chance to wound, 16% chance to fail an armor save, and 6 wounds to get through, it would take about 64 BS4 Krak Missile shots to kill a Tyrannofex.
Now, one weapon type that will absolutely each Tyrranofexes for lunch is Grav weapons, especially Grav Cannons with Grav Amps… at BS4, it only takes about 9 Grav Cannon/Amp shots to kill a Tyrannofex, so steer clear of Centurions or deal with them before the Tyrranocyte comes in from reserve.
Aside froms it shooting and close combat output and the damage it can absorb from enemy attacks, perhaps the biggest advantage of dropping 1-3 Tyrranofexes into your opponent’s DZ using Tyrranocytes is the psychological element… seeing three massive Tyranid MCs with tons of wounds and serious close combat threat suddenly right up against his army will make many players overeact, abandon their game-plan, forget to deal with the rest of your army, or all of the above, allowing you to exploit their decision-making. Put another way, you could say that the “Tyrranofex Drop” is a shock tactic as much as it is a way to get these MCs into the fight!