The Shadow in the Warp
Of all the creatures in the Tyranid army, the Hive Tyrant is truly the most horrifying to face. Sure, the Carnifex is stronger, the Trygon can burst out of the ground without warning, and the Tyrannofex has a gun larger than most other Tyranid creatures, but it's the Hive Tyrant that will really inspire terror in your enemies. Flee for your lives terror.
So why have they gained such a terrifying reputation? The Hive Tyrant is a close combat monster, pure and simple. Every inch of its body is designed to kill enemy warriors with impunity, from the razor-sharp armour plates covering its body, to the impaling spike on its forehead and the many bioweapons that it carries into battle. Come up against this beast and you're likely to find yourself outclassed in every respect - they're tough, fast and very, very good at despatching their foes with minimal effort and to maximum effect.
But close combat is not their only area of expertise - they are also very competent psykers. With just a glance, a Hive Tyrant can wither the flesh of nearby enemy troops and use it to regenerate any damage they may have already sustained. Alternatively, why not just scare the living daylights out of your enemies instead? A Psychic Scream from a Hive Tyrant is something akin to thousands of fingernails being scraped down a very long blackboard (for those of you too young to remember the sound of fingernails down a blackboard, make sure you ask your parents about it - I'm sure they'll be willing to demonstrate it).
And if that wasn't enough, there are plenty of biomorphs available to a Hive Tyrant to beef them up a bit. Yes, that's right, if you didn't think they were hard enough already, why not give them a couple of upgrades to make them ultra-nasty. How about giving them an Armoured Shell to stop heavy weaponry? Or maybe upgrade their spore chimneys to emit a toxin miasma and choke your foes to death? Or why not just give it wings and fly into combat - that should give your opponents a bit of a fright early in the game.
So if you haven't got a Hive Tyrant in your Tyranid army yet, then make sure you add one to it soon, because they will cause first rate devastation on the battlefield. And if you don't collect Tyranids? Well, you're going to need some seriously big guns or a team of utterly Fearless (potentially insane) warriors to take it on in combat.